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!standard G (00) 03-05-22 AI95-00296/02
!class amendment 02-06-07
!status received 02-06-07
!priority Medium
!difficulty Medium
!subject Vector and matrix operations

!summary

The vector and matrix operations in ISO/IEC 13813 plus related operations are added to Ada.Numerics in Annex G.

!problem

A number of secondary standards for Ada 83 were produced for the numerics area. Most of the functionality of these standards was incorporated into Ada 95 (some in the core language and some in the Numerics Annex) but two packages from ISO/IEC 13813 were not. These are generic packages for the manipulation of real and complex vectors and matrices.

The UK was asked to review the situation and to make a recommendation; they recommended that if Ada were amended then consideration should be given to including the packages within the Numerics annex.

The packages can be implemented entirely in Ada and thus present little burden to implementors. Providing secondary standards has not proved satisfactory because they are not sufficiently visible to the user community as a whole.

!proposal

It is proposed that two generic packages be added to the numerics annex. They are Ada.Numerics.Generic_Real_Arrays and Ada.Numerics.Generic_Complex_Arrays. They are included as a new subclause G.3 in order to avoid excessive renumbering of other clauses.

In addition to the main facilities of 13813, these packages also include operations for matrix inversion and determinants. Furthermore, child packages provide subprograms for the determination of eigenvalues and eigenvectors.

!wording

Add a new clause G.3 as follows

G.3 Vector and matrix manipulation

Types and operations for the manipulation of real vectors and matrices are provided in Generic_Real_Arrays, which is defined in G.3.1. Types and operations for the manipulation of complex vectors and matrices are provided in Generic_Complex_Arrays, which is defined in G.3.2. Both of these library units are generic children of the predefined package Numerics (see A.5). Nongeneric equivalents of these packages for each of the predefined floating point types are also provided as children of Numerics.

generic child packages for the determination of eigenvalues and eigenvectors are defined in G.3.3.

G.3.1 Real Vectors and Matrices

The generic library package Numerics.Generic_Real_Arrays has the following declaration:

generic type Real is digits <>; package Ada.Numerics.Generic_Real_Arrays is pragma Pure(Generic_Real_Arrays);

-- Types

type Real_Vector is array (Integer range <>) of Real'Base; type Real_Matrix is array (Integer range <>, Integer range <>) of Real'Base;

-- Real_Vector additive operations

function "+" (Right : Real_Vector) return Real_Vector; function "-" (Right : Real_Vector) return Real_Vector; function "abs" (Right : Real_Vector) return Real_Vector;

function "+" (Left, Right : Real_Vector) return Real_Vector; function "-" (Left, Right : Real_Vector) return Real_Vector;

-- Real_Vector scaling operations

function "*" (Left : Real'Base; Right : Real_Vector) return Real_Vector; function "*" (Left : Real_Vector; Right : Real'Base) return Real_Vector; function "/" (Left : Real_Vector; Right : Real'Base) return Real_Vector;

-- Inner, Outer and Vector products

function "*" (Left, Right : Real_Vector) return Real'Base; function "*" (Left, Right : Real_Vector) return Real_Matrix; function "*" (Left, Right : Real_Vector) return Real_Vector;

-- Other Real_Vector operations

function Unit_Vector (Index : Integer; Order : Positive; First : Integer := 1) return Real_Vector;

-- Real_Matrix arithmetic operations

function "+" (Right : Real_Matrix) return Real_Matrix; function "-" (Right : Real_Matrix) return Real_Matrix; function "abs" (Right : Real_Matrix) return Real_Matrix; function Transpose (X : Real_Matrix) return Real_Matrix;

function "+" (Left, Right : Real_Matrix) return Real_Matrix; function "-" (Left, Right : Real_Matrix) return Real_Matrix; function "*" (Left, Right : Real_Matrix) return Real_Matrix;

function "*" (Left : Real_Vector; Right : Real_Matrix) return Real_Vector; function "*" (Left : Real_Matrix; Right : Real_Vector) return Real_Vector;

-- Real_Matrix scaling operations

function "*" (Left : Real'Base; Right : Real_Matrix) return Real_Matrix; function "*" (Left : Real_Matrix; Right : Real'Base) return Real_Matrix; function "/" (Left : Real_Matrix; Right : Real'Base) return Real_Matrix;

-- Real_Matrix inversion and related operations

function Solve (A : Real_Matrix; X: Real_Vector) return Real_Vector; function Solve (A, X : Real_Matrix) return Real_Matrix; function Inverse (A : Real_Matrix) return Real_Matrix; function Determinant (A : Real_Matrix) return Real'Base;

-- Other Real_Matrix operations

function Unit_Matrix (Order : Positive; First_1, First_2 : Integer := 1) return Real_Matrix;

end Ada.Numerics.Generic_Real_Arrays;

The library package Numerics.Real_Arrays is declared pure and defines the same types and subprograms as Numerics.Generic_Real_Arrays, except that the predefined type Float is systematically substituted for Real'Base throughout. Nongeneric equivalents for each of the other predefined floating point types are defined similarly, with the names Numerics.Short_Real_Arrays, Numerics.Long_Real_Arrays, etc.

Two types are defined and exported by Ada.Numerics.Generic_Real_Arrays. The composite type Real_Vector is provided to represent a vector with components of type Real; it is defined as an unconstrained, one-dimensional array with an index of type Integer. The composite type Real_Matrix is provided to represent a matrix with components of type Real; it is defined as an unconstrained, two-dimensional array with indices of type Integer.

The effect of the various functions is as described below. In most cases the functions are described in terms of corresponding scalar operations of the type Real; any exception raised by those operations is propagated by the array operation. Moreover the accuracy of the result for each individual component is as defined for the scalar operation unless stated otherwise.

In the case of those operations which are defined to involve an inner product, Constraint_Error may be raised if an intermediate result is outside the range of Real'Base even though the mathematical final result would not be.

function "+" (Right : Real_Vector) return Real_Vector; function "-" (Right : Real_Vector) return Real_Vector; function "abs" (Right : Real_Vector) return Real_Vector;

Each operation returns the result of applying the corresponding operation of the type Real to each component of Right. The index range of the result is Right'Range.

function "+" (Left, Right : Real_Vector) return Real_Vector; function "-" (Left, Right : Real_Vector) return Real_Vector;

Each operation returns the result of applying the corresponding operation of the type Real to each component of Left and the matching component of Right. The index range of the result is Left'Range. The exception Constraint_Error is raised if Left'Length is not equal to Right'Length.

function "*" (Left : Real'Base; Right : Real_Vector) return Real_Vector;

This operation returns the result of multiplying each component of Right by the scalar Left using the "*" operation of the type Real. The index range of the result is Right'Range.

function "*" (Left : Real_Vector; Right : Real'Base) return Real_Vector; function "/" (Left : Real_Vector; Right : Real'Base) return Real_Vector;

Each operation returns the result of applying the corresponding operation of the type Real to each component of Left and to the scalar Right. The index range of the result is Left'Range.

function "*" (Left, Right : Real_Vector) return Real'Base;

This operation returns the inner product of Left and Right. The exception Constraint_Error is raised if Left'Length is not equal to Right'Length. This operation involves an inner product.

function "*" (Left, Right : Real_Vector) return Real_Matrix;

This operation returns the outer product of a (column) vector Left by a (row) vector Right using the appropriate operation "*" of the type Real for computing the individual components. The first and second index ranges of the matrix result are Left'Range and Right'Range respectively.

function "*" (Left, Right : Real_Vector) return Real_Vector;

This operation returns the vector product of Left and Right. The exception Constraint_Error is raised if Left'Length and Right'Length are not equal to 3. The index range of the result is Left'Range.

?? I am not sure about vector product. It only exists in three dimensions and is really a skew-symmetric tensor.

function Unit_Vector (Index : Integer; Order : Positive; First : Integer := 1) return Real_Vector;

This function returns a "unit vector" with Order components and a lower bound of First. All components are set to 0.0 except for the Index component which is set to 1.0. The exception Constraint_Error is raised if Index < First, Index > First + Order - 1 or if First + Order - 1 > Integer'Last.

function "+" (Right : Real_Matrix) return Real_Matrix; function "-" (Right : Real_Matrix) return Real_Matrix; function "abs" (Right : Real_Matrix) return Real_Matrix;

Each operation returns the result of applying the corresponding operation of the type Real to each component of Right. The index ranges of the result are those of Right.

function Transpose (X : Real_Matrix) return Real_Matrix;

This function returns the transpose of a matrix X. The first and second index ranges of the result are X'Range(2) and X'Range(1) respectively.

function "+" (Left, Right : Real_Matrix) return Real_Matrix; function "-" (Left, Right : Real_Matrix) return Real_Matrix;

Each operation returns the result of applying the corresponding operation of type Real to each component of Left and the matching component of Right. The index ranges of the result are those of Left. The exception Constraint_Error is raised if Left'Length(1) is not equal to Right'Length(1) or Left'Length(2) is not equal to Right'Length(2).

function "*" (Left, Right : Real_Matrix) return Real_Matrix;

This operation provides the standard mathematical operation for matrix multiplication. The first and second index ranges of the result are Left'Range(1) and Right'Range(2) respectively. The exception Constraint_Error is raised if Left'Length(2) is not equal to Right'Length(1). This operation involves inner products.

function "*" (Left : Real_Vector; Right : Real_Matrix) return Real_Vector;

This operation provides the standard mathematical operation for multiplication of a (row) vector Left by a matrix Right. The index range of the (row) vector result is Right'Range(2). The exception Constraint_Error is raised if Left'Length is not equal to Right'Length(1). This operation involves inner products.

function "*" (Left : Real_Matrix; Right : Real_Vector) return Real_Vector;

This operation provides the standard mathematical operation for multiplication of a matrix Left by a (column) vector Right. The index range of the (column) vector result is Left'Range(1). The exception Constraint_Error is raised if Left'Length(2) is not equal to Right'Length. This operation involves inner products.

function "*" (Left : Real'Base; Right : Real_Matrix) return Real_Matrix;

This operation returns the result of multiplying each component of Right by the scalar Left using the "*" operation of the type Real. The index ranges of the matrix result are those of Right.

function "*" (Left : Real_Matrix; Right : Real'Base) return Real_Matrix; function "/" (Left : Real_Matrix; Right : Real'Base) return Real_Matrix;

Each operation returns the result of applying the corresponding operation of the type Real to each component of Left and to the scalar Right. The index ranges of the matrix result are those of Left.

function Solve (A : Real_Matrix; X: Real_Vector) return Real_Vector;

This function returns a vector Y such that X is (nearly) equal to A * Y. This is the standard mathematical operation for solving a single set of linear equations. The index range of the result is X'Range. Constraint_Error is raised if A'Length(1), A'Length(2) and X'Length are not equal. Constraint_Error is raised if the matrix A is ill-conditioned.

function Solve (A, X : Real_Matrix) return Real_Matrix;

This function returns a matrix Y such that X is (nearly) equal to A * Y. This is the standard mathematical operation for solving several sets of linear equations. The index ranges of the result are those of X. Constraint_Error is raised if A'Length(1), A'Length(2) and X'Length(1) are not equal. Constraint_Error is raised if the matrix A is ill-conditioned.

function Inverse (A : Real_Matrix) return Real_Matrix;

This function returns a matrix B such that A * B is (nearly) the unit matrix. The index ranges of the result are those of A. Constraint_Error is raised if A'Length(1) is not equal to A'Length(2). Constraint_Error is raised if the matrix A is ill-conditioned.

function Determinant (A : Real_Matrix) return Real'Base;

This function returns the determinant of the matrix A. Constraint_Error is raised if A'Length(1) is not equal to A'Length(2).

function Unit_Matrix (Order : Positive; First_1, First_2 : Integer := 1) return Real_Matrix;

This function returns a square "unit matrix" with Order**2 components and lower bounds of First_1 and First_2 (for the first and second index ranges respectively). All components are set to 0.0 except for the main diagonal, whose components are set to 1.0. The exception Constraint_Error is raised if First_1 + Order - 1 > Integer'Last or First_2 + Order - 1 > Integer'Last.

Implementation Requirements

Accuracy requirements for the functions Solve, Inverse and Determinant are implementation defined.

For operations not involving an inner product, the accuracy requirements are those of the corresponding operations of the type Real in both the strict mode and the relaxed mode (see G.2).

?? This doesn't really cover vector product but I might delete it anyway.

For operations involving an inner product, no requirements are specified in the relaxed mode. In the strict mode the acuracy should be at least that of the canonical implementation of multiplication and addition using the corresponding operations of type Real'Base and performing the cumulative addition using ascending indices. Implementations shall document any techniques used to reduce cancellation errors such as extended precision arithmetic.

Implementation Permissions

The nongeneric equivalent packages may, but need not, be actual instantiations of the generic package for the appropriate predefined type.

Implementation Advice

Implementations should implement the Solve and Inverse functions using established techniques such as Gauss-Seidel with Interchanges.

It is not the intention that any special provision should be made to determine whether a matrix is ill-conditioned or not. The naturally occuring division by zero or overflow which will result from executing these functions with an ill-conditioned matrix and thus raise Constraint_Error is sufficient.

G.3.2 Complex Vectors and Matrices

The generic library package Numerics.Generic_Complex_Arrays has the following declaration:

with Ada.Numerics.Generic_Real_Arrays, Ada.Numerics.Generic_Complex_Types; generic with package Real_Arrays is new Ada.Numerics.Generic_Real_Arrays (<>); use Real_Arrays; with package Complex_Types is new Ada.Numerics.Generic_Complex_Types (Real); use Complex_Types; package Ada.Numerics.Generic_Complex_Arrays is pragma Pure(Generic_Complex_Arrays);

-- Types

type Complex_Vector is array (Integer range <>) of Complex; type Complex_Matrix is array (Integer range <>, Integer range <>) of Complex;

-- Complex_Vector selection, conversion and composition operations

function Re (X : Complex_Vector) return Real_Vector; function Im (X : Complex_Vector) return Real_Vector;

procedure Set_Re (X : in out Complex_Vector; Re : in Real_Vector); procedure Set_Im (X : in out Complex_Vector; Im : in Real_Vector);

function Compose_From_Cartesian (Re : Real_Vector) return Complex_Vector; function Compose_From_Cartesian (Re, Im : Real_Vector) return Complex_Vector;

function Modulus (X : Complex_Vector) return Real_Vector; function "abs" (Right : Complex_Vector) return Real_Vector renames Modulus; function Argument (X : Complex_Vector) return Real_Vector; function Argument (X : Complex_Vector; Cycle : Real'Base) return Real_Vector;

function Compose_From_Polar (Modulus, Argument : Real_Vector) return Complex_Vector; function Compose_From_Polar (Modulus, Argument : Real_Vector; Cycle : Real'Base) return Complex_Vector;

-- Complex_Vector additive operations

function "+" (Right : Complex_Vector) return Complex_Vector; function "-" (Right : Complex_Vector) return Complex_Vector; function Conjugate (X : Complex_Vector) return Complex_Vector;

function "+" (Left, Right : Complex_Vector) return Complex_Vector; function "-" (Left, Right : Complex_Vector) return Complex_Vector;

-- Mixed Real_Vector and Complex_Vector additive operations

function "+" (Left : Real_Vector; Right : Complex_Vector) return Complex_Vector; function "+" (Left : Complex_Vector; Right : Real_Vector) return Complex_Vector; function "-" (Left : Real_Vector; Right : Complex_Vector) return Complex_Vector; function "-" (Left : Complex_Vector; Right : Real_Vector) return Complex_Vector;

-- Complex_Vector scaling operations

function "*" (Left : Complex; Right : Complex_Vector) return Complex_Vector; function "*" (Left : Complex_Vector; Right : Complex) return Complex_Vector; function "/" (Left : Complex_Vector; Right : Complex) return Complex_Vector;

function "*" (Left : Real'Base; Right : Complex_Vector) return Complex_Vector; function "*" (Left : Complex_Vector; Right : Real'Base) return Complex_Vector; function "/" (Left : Complex_Vector; Right : Real'Base) return Complex_Vector;

-- Inner, Outer and Vector products

function "*" (Left, Right : Complex_Vector) return Complex; function "*" (Left : Real_Vector; Right : Complex_Vector) return Complex; function "*" (Left : Complex_Vector; Right : Real_Vector) return Complex;

function "*" (Left, Right : Complex_Vector) return Complex_Matrix; function "*" (Left : Real_Vector; Right : Complex_Vector) return Complex_Matrix; function "*" (Left : Complex_Vector; Right : Real_Vector) return Complex_Matrix;

function "*" (Left, Right : Complex_Vector) return Complex_Vector; function "*" (Left : Real_Vector; Right : Complex_Vector) return Complex_Vector; function "*" (Left : Complex_Vector; Right : Real_Vector) return Complex_Vector;

-- Other Complex_Vector operations

function Unit_Vector (Index : Integer; Order : Positive; First : Integer := 1) return Complex_Vector;

-- Complex_Matrix selection, conversion and composition operations

function Re (X : Complex_Matrix) return Real_Matrix; function Im (X : Complex_Matrix) return Real_Matrix;

procedure Set_Re (X : in out Complex_Matrix; Re : in Real_Matrix); procedure Set_Im (X : in out Complex_Matrix; Im : in Real_Matrix);

function Compose_From_Cartesian (Re : Real_Matrix) return Complex_Matrix; function Compose_From_Cartesian (Re, Im : Real_Matrix) return Complex_Matrix;

function Modulus (X : Complex_Matrix) return Real_Matrix; function "abs" (Right : Complex_Matrix) return Real_Matrix renames Modulus;

function Argument (X : Complex_Matrix) return Real_Matrix; function Argument (X : Complex_Matrix; Cycle : Real'Base) return Real_Matrix;

function Compose_From_Polar (Modulus, Argument : Real_Matrix) return Complex_Matrix; function Compose_From_Polar (Modulus, Argument : Real_Matrix; Cycle : Real'Base) return Complex_Matrix;

-- Complex_Matrix arithmetic operations

function "+" (Right : Complex_Matrix) return Complex_Matrix; function "-" (Right : Complex_Matrix) return Complex_Matrix; function Conjugate (X : Complex_Matrix) return Complex_Matrix; function Transpose (X : Complex_Matrix) return Complex_Matrix;

function "+" (Left, Right : Complex_Matrix) return Complex_Matrix; function "-" (Left, Right : Complex_Matrix) return Complex_Matrix; function "*" (Left, Right : Complex_Matrix) return Complex_Matrix;

function "*" (Left : Complex_Vector; Right : Complex_Matrix) return Complex_Vector; function "*" (Left : Complex_Matrix; Right : Complex_Vector) return Complex_Vector;

-- Mixed Real_Matrix and Complex_Matrix arithmetic operations

function "+" (Left : Real_Matrix; Right : Complex_Matrix) return Complex_Matrix; function "+" (Left : Complex_Matrix; Right : Real_Matrix) return Complex_Matrix; function "-" (Left : Real_Matrix; Right : Complex_Matrix) return Complex_Matrix; function "-" (Left : Complex_Matrix; Right : Real_Matrix) return Complex_Matrix; function "*" (Left : Real_Matrix; Right : Complex_Matrix) return Complex_Matrix; function "*" (Left : Complex_Matrix; Right : Real_Matrix) return Complex_Matrix;

function "*" (Left : Real_Vector; Right : Complex_Matrix) return Complex_Vector; function "*" (Left : Complex_Vector; Right : Real_Matrix) return Complex_Vector; function "*" (Left : Real_Matrix; Right : Complex_Vector) return Complex_Vector; function "*" (Left : Complex_Matrix; Right : Real_Vector) return Complex_Vector;

-- Complex_Matrix scaling operations

function "*" (Left : Complex; Right : Complex_Matrix) return Complex_Matrix; function "*" (Left : Complex_Matrix; Right : Complex) return Complex_Matrix; function "/" (Left : Complex_Matrix; Right : Complex) return Complex_Matrix;

function "*" (Left : Real'Base; Right : Complex_Matrix) return Complex_Matrix; function "*" (Left : Complex_Matrix; Right : Real'Base) return Complex_Matrix; function "/" (Left : Complex_Matrix; Right : Real'Base) return Complex_Matrix;

-- Complex_Matrix inversion and related operations

function Solve (A : Complex_Matrix; X: Complex_Vector) return Complex_Vector; function Solve (A, X : Complex_Matrix) return Complex_Matrix; function Inverse (A : Complex_Matrix) return Complex_Matrix; function Determinant (A : Complex_Matrix) return Complex;

?? I have not added mixed real and complex for Solve.

-- Other Complex_Matrix operations

function Unit_Matrix (Order : Positive;

First_1, First_2 : Integer := 1)

return Complex_Matrix;

end Ada.Numerics.Generic_Complex_Arrays;

The library package Numerics.Complex_Arrays is declared pure and defines the same types and subprograms as Numerics.Generic_Complex_Arrays, except that the predefined type Float is systematically substituted for Real'Base, and the Real_Vector and Real_Matrix types exported by Numerics.Real_Arrays are systematically substituted for Real_Vector and Real_Matrix, and the Complex and Imaginary types exported by Numerics.Complex_Types are systematically substituted for Complex and Imaginary, throughout. Nongeneric equivalents for each of the other predefined floating point types are defined similarly, with the names Numerics.Short_Complex_Arrays, Numerics.Long_Complex_Arrays, etc.

?? I based this text on that in G.1.2(9/1). However this clause (ie G.3.2) doesn't seem to use Imaginary but I left it in.

Two types are defined and exported by Ada.Numerics.Generic_Complex_Arrays. The composite type Complex_Vector is provided to represent a vector with components of type Complex; it is defined as an unconstrained one-dimensional array with an index of type Integer. The composite type Complex_Matrix is provided to represent a matrix with components of type Complex; it is defined as an unconstrained, two-dimensional array with indices of type Integer.

The effect of the various subprograms is as described below. In many cases they are described in terms of corresponding scalar operations in Numerics.Generic_Complex_Types. Any exception raised by those operations is propagated by the array subprogram. Moreover any constraints on the parameters and the accuracy of the result for each individual component is as defined for the scalar operation.

In the case of those operations which are defined to involve an inner product, Constraint_Error may be raised if an intermediate result has a component outside the range of Real'Base even though the final mathematical result would not.

function Re (X : Complex_Vector) return Real_Vector; function Im (X : Complex_Vector) return Real_Vector;

Each function returns a vector of the specified cartesian components of X. The index range of the result is X'Range.

procedure Set_Re (X : in out Complex_Vector; Re : in Real_Vector); procedure Set_Im (X : in out Complex_Vector; Im : in Real_Vector);

Each procedure replaces the specified (cartesian) component of each of the components of X by the value of the matching component of Re or Im; the other (cartesian) component of each of the components is unchanged. The exception Constraint_Error is raised if X'Length is not equal to Re'Length and if X'Length is not equal to Im'Length.

function Compose_From_Cartesian (Re : Real_Vector) return Complex_Vector; function Compose_From_Cartesian (Re, Im : Real_Vector) return Complex_Vector;

Each function constructs a vector of Complex results (in cartesian representation) formed from given vectors of cartesian components; when only the real components are given, imaginary components of zero are assumed. The index range of the result is Re'Range. The exception Constraint_Error is raised if Re'Length is not equal to Im'Length.

Each function calculates and returns a vector of the specified polar components of X or Right using the corresponding function in Numerics.Generic_Complex_Types. The index range of the result is X'Range or Right'Range.

Each function constructs a vector of Complex results (in cartesian representation) formed from given vectors of polar components using the corresponding function in Numerics.Generic_Complex_Types on matching components of Modulus and Argument. The index range of the result is Modulus'Range. The exception Constraint_Error is raised if Modulus'Length is not equal to Argument'Length.

function "+" (Right : Complex_Vector) return Complex_Vector; function "-" (Right : Complex_Vector) return Complex_Vector;

Each operation returns the result of applying the corresponding operation in Numerics.Generic_Complex_Types to each component of Right. The index range of the result is Right'Range.

function Conjugate (X : Complex_Vector) return Complex_Vector;

This function returns the result of applying the appropriate function Conjugate in Numerics.Generic_Complex_Types to each component of X. The index range of the result is X'Range.

function "+" (Left, Right : Complex_Vector) return Complex_Vector; function "-" (Left, Right : Complex_Vector) return Complex_Vector;

function "+" (Left : Real_Vector;

Right : Complex_Vector) return Complex_Vector;

function "+" (Left : Complex_Vector;

Right : Real_Vector) return Complex_Vector;

function "-" (Left : Real_Vector;

Right : Complex_Vector) return Complex_Vector;

function "-" (Left : Complex_Vector;

Right : Real_Vector) return Complex_Vector;

Each operation returns the result of applying the corresponding operation in Numerics.Generic_Complex_Types to each component of Left and the matching component of Right. The index range of the result is Left'Range. The exception Constraint_Error is raised if Left'Length is not equal to Right'Length.

function "*" (Left : Complex; Right : Complex_Vector) return Complex_Vector;

This operation returns the result of multiplying each component of Right by the complex number Left using the appropriate operation "*" in Numerics.Generic_Complex_Types. The index range of the result is Right'Range.

function "*" (Left : Complex_Vector; Right : Complex) return Complex_Vector; function "/" (Left : Complex_Vector; Right : Complex) return Complex_Vector;

Each operation returns the result of applying the corresponding operation in Numerics.Generic_Complex_Types to each component of the vector Left and the complex number Right. The index range of the result is Left'Range.

function "*" (Left : Real'Base; Right : Complex_Vector) return Complex_Vector;

This operation returns the result of multiplying each component of Right by the real number Left using the appropriate operation "*" in Numerics.Generic_Complex_Types. The index range of the result is Right'Range.

function "*" (Left : Complex_Vector; Right : Real'Base) return Complex_Vector; function "/" (Left : Complex_Vector; Right : Real'Base) return Complex_Vector;

Each operation returns the result of applying the corresponding operation in Numerics.Generic_Complex_Types to each component of the vector Left and the real number Right. The index range of the result is Left'Range.

function "*" (Left, Right : Complex_Vector) return Complex; function "*" (Left : Real_Vector; Right : Complex_Vector) return Complex; function "*" (Left : Complex_Vector; Right : Real_Vector) return Complex;

Each operation returns the inner product of Left and Right. The exception Constraint_Error is raised if Left'Length is not equal to Right'Length. These operations involve an inner product.

function "*" (Left, Right : Complex_Vector) return Complex_Matrix; function "*" (Left : Real_Vector;

Right : Complex_Vector) return Complex_Matrix;

function "*" (Left : Complex_Vector;

Right : Real_Vector) return Complex_Matrix;

Each operation returns the outer product of a (column) vector Left by a (row) vector Right using the appropriate operation "*" in Numerics.Generic_Complex_Types for computing the individual components. The first and second index ranges of the matrix result are Left'Range and Right'Range respectively.

function "*" (Left, Right : Complex_Vector) return Complex_Vector; function "*" (Left : Real_Vector;

Right : Complex_Vector) return Complex_Vector;

function "*" (Left : Complex_Vector;

Right : Real_Vector) return Complex_Vector;

Each operation returns the vector product of Left and Right. The exception Constraint_Error is raised if Left'Length and Right'Length are not equal to 3. The index range of the result is Left'Range.

function Unit_Vector (Index : Integer; Order : Positive; First : Integer := 1) return Complex_Vector;

This function returns a "unit vector" with Order components and a lower bound of First. All components are set to (0.0,0.0) except for the Index component which is set to (1.0,0.0). The exception Constraint_Error is raised if Index < First, Index > First + Order - 1, or if First + Order - 1 > Integer'Last.

function Re (X : Complex_Matrix) return Real_Matrix; function Im (X : Complex_Matrix) return Real_Matrix;

Each function returns a matrix of the specified cartesian components of X. The index ranges of the result are those of X.

procedure Set_Re (X : in out Complex_Matrix; Re : in Real_Matrix); procedure Set_Im (X : in out Complex_Matrix; Im : in Real_Matrix);

Each procedure replaces the specified (cartesian) component of each of the components of X by the value of the matching component of Re or Im; the other (cartesian) component of each of the components is unchanged. The exception Constraint_Error is raised if X'Length(1) is not equal to Re'Length(1) or X'Length(2) is not equal to Re'Length(2) and if X'Length(1) is not equal to Im'Length(1) or X'Length(2) is not equal to Im'Length(2).

function Compose_From_Cartesian (Re : Real_Matrix) return Complex_Matrix; function Compose_From_Cartesian (Re, Im : Real_Matrix) return Complex_Matrix;

Each function constructs a matrix of Complex results (in cartesian representation) formed from given matrices of cartesian components; when only the real components are given, imaginary components of zero are assumed. The index ranges of the result are those of Re. The exception Constraint_Error is raised if Re'Length(1) is not equal to Im'Length(1) or Re'Length(2) is not equal to Im'Length(2).

function Modulus (X : Complex_Matrix) return Real_Matrix; function "abs" (Right : Complex_Matrix) return Real_Matrix renames Modulus; function Argument (X : Complex_Matrix) return Real_Matrix; function Argument (X : Complex_Matrix; Cycle : Real'Base) return Real_Matrix;

Each function calculates and returns a matrix of the specified polar components of X or Right using the corresponding function in Numerics.Generic_Complex_Types. The index ranges of the result are those of X or Right.

Each function constructs a matrix of Complex results (in cartesian representation) formed from given matrices of polar components using the corresponding function in Numerics.Generic_Complex_Types on matching components of Modulus and Argument. The index ranges of the result are those of Modulus. The exception Constraint_Error is raised if Modulus'Length(1) is not equal to Argument'Length(1) or Modulus'Length(2) is not equal to Argument'Length(2).

function "+" (Right : Complex_Matrix) return Complex_Matrix; function "-" (Right : Complex_Matrix) return Complex_Matrix;

Each operation returns the result of applying the corresponding operation in Numerics.Generic_Complex_Types to each component of Right. The index ranges of the result are those of Right.

function Conjugate (X : Complex_Matrix) return Complex_Matrix;

This function returns the result of applying the appropriate function Conjugate in Numerics.Generic_Complex_Types to each component of X. The index ranges of the result are those of X.

function Transpose (X : Complex_Matrix) return Complex_Matrix;

This function returns the transpose of a matrix X. The first and second index ranges of the result are X'Range(2) and X'Range(1) respectively.

function "+" (Left, Right : Complex_Matrix) return Complex_Matrix; function "-" (Left, Right : Complex_Matrix) return Complex_Matrix;

Each operation returns the result of applying the corresponding operation in Numerics.Generic_Complex_Types to each component of Left and the matching component of Right. The index ranges of the result are those of Left. The exception Constraint_Error is raised if Left'Length(1) is not equal to Right'Length(1) or Left'Length(2) is not equal to Right'Length(2).

function "*" (Left, Right : Complex_Matrix) return Complex_Matrix;

function "*" (Left : Complex_Vector;

Right : Complex_Matrix) return Complex_Vector;

function "*" (Left : Complex_Matrix;

Right : Complex_Vector) return Complex_Vector;

function "+" (Left : Real_Matrix;

Right : Complex_Matrix) return Complex_Matrix;

function "+" (Left : Complex_Matrix;

Right : Real_Matrix) return Complex_Matrix;

function "-" (Left : Real_Matrix;

Right : Complex_Matrix) return Complex_Matrix;

function "-" (Left : Complex_Matrix;

Right : Real_Matrix) return Complex_Matrix;

Each operation returns the result of applying the corresponding operation in Numerics.Generic_Complex_Types to each component of Left and the matching component of Right. The index ranges of the result are those of Left. The exception Constraint_Error is raised if Left'Length(1) is not equal to Right'Length(1) or Left'Length(2) is not equal to Right'Length(2).

function "*" (Left : Real_Matrix;

Right : Complex_Matrix) return Complex_Matrix;

function "*" (Left : Complex_Matrix;

Right : Real_Matrix) return Complex_Matrix;

Each operation provides the standard mathematical operation for matrix multiplication. The first and second index ranges of the result are Left'Range(1) and Right'Range(2) respectively. The exception Constraint_Error is raised if Left'Length(2) is not equal to Right'Length(1). These operations involve inner products.

function "*" (Left : Real_Vector;

Right : Complex_Matrix) return Complex_Vector;

function "*" (Left : Complex_Vector;

Right : Real_Matrix) return Complex_Vector;

Each operation provides the standard mathematical operation for multiplication of a (row) vector Left by a matrix Right. The index range of the (row) vector result is Right'Range(2). The exception Constraint_Error is raised if Left'Length is not equal to Right'Length(1). These operations involve inner products.

function "*" (Left : Real_Matrix;

Right : Complex_Vector) return Complex_Vector;

function "*" (Left : Complex_Matrix;

Right : Real_Vector) return Complex_Vector;

Each operation provides the standard mathematical operation for multiplication of a matrix Left by a (column) vector Right. The index range of the (column) vector result is Left'Range(1). The exception Constraint_Error is raised if Left'Length(2) is not equal to Right'Length. These operations involve inner products.

function "*" (Left : Complex; Right : Complex_Matrix) return Complex_Matrix;

function "*" (Left : Complex_Matrix; Right : Complex) return Complex_Matrix; function "/" (Left : Complex_Matrix; Right : Complex) return Complex_Matrix;

Each operation returns the result of applying the corresponding operation in Numerics.Generic_Complex_Types to each component of the matrix Left and the complex number Right. The index ranges of the result are those of Left.

function "*" (Left : Real'Base; Right : Complex_Matrix) return Complex_Matrix;

function "*" (Left : Complex_Matrix; Right : Real'Base) return Complex_Matrix; function "/" (Left : Complex_Matrix; Right : Real'Base) return Complex_Matrix;

Each operation returns the result of applying the corresponding operation in Numerics.Generic_Complex_Types to each component of the matrix Left and the scalar Right. The index ranges of the result are those of Left.

function Solve (A : Complex_Matrix; X: Complex_Vector) return Complex_Vector;

function Solve (A, X : Complex_Matrix) return Complex_Matrix;

function Inverse (A : Complex_Matrix) return Complex_Matrix;

function Determinant (A : Complex_Matrix) return Complex;

This function returns the determinant of the matrix A. Constraint_Error is raised if A'Length(1) is not equal to A'Length(2).

function Unit_Matrix (Order : Positive; First_1, First_2 : Integer := 1) return Complex_Matrix;

This function returns a square "unit matrix" with Order**2 components and lower bounds of First_1 and First_2 (for the first and second index ranges respectively). All components are set to (0.0,0.0) except for the main diagonal, whose components are set to (1.0,0.0). The exception Constraint_Error is raised if First_1 + Order - 1 > Integer'Last or First_2 + Order - 1 > Integer'Last.

Implementation Requirements

Accuracy requirements for the functions Solve, Inverse and Determinant are implementation defined.

For operations not involving an inner product, the accuracy requirements are those of the corresponding operations of the type Real'Base and Complex in both the strict mode and the relaxed mode (see G.2).

?? This doesn't really cover vector product but I might delete it anyway.

For operations involving an inner product, no requirements are specified in the relaxed mode. In the strict mode the acuracy should be at least that of the canonical implementation of multiplication and addition using the corresponding operations of type Real'Base and Complex and performing the cumulative addition using ascending indices. Implementations shall document any techniques used to reduce cancellation errors such as extended precision arithmetic.

Implementation Permissions

The nongeneric equivalent packages may, but need not, be actual instantiations of the generic package for the appropriate predefined type.

Although many operations are defined in terms of operations from Numerics.Generic_Complex_Types, they need not be implemented by calling those operations provided that the effect is the same.

Implementation Advice

Implementations should implement the Solve and Inverse functions using established techniques such as Gauss-Seidel with Interchanges.

Implementations should not perform operations on mixed complex and real operands by first converting the real operand to complex. See G.1.1(56,57).

G.3.3 Eigensystems of Matrices

Eigenvalues and eigenvectors of a real symmetric matrix are computed using subprograms in the child package Ada.Numerics.Generic_Real_Arrays.Eigen whose declaration is:

generic package Ada.Numerics.Generic_Real_Arrays.Eigen is pragma Pure(Eigen);

function Values(A : Real_Matrix) return Real_Vector;

procedure Values_And_Vectors(A : in Real_Matrix; Values : out Real_Vector; Vectors : out Real_Matrix);

end Ada.Numerics.Generic_Real_Arrays.Eigen;

The library package Numerics.Real_Arrays.Eigen is declared pure and defines the same subprograms as Numerics.Generic_Real_Arrays.Eigen, except that the predefined type Float is systematically substituted for Real'Base throughout. Nongeneric equivalents for each of the other predefined floating point types are defined similarly, with the names Numerics.Short_Real_Arrays.Eigen, Numerics.Long_Real_Arrays.Eigen, etc.

The effect of the subprograms is as described below.

function Values(A : Real_Matrix) return Real_Vector;

This function returns the eigenvalues of the symmetric matrix A as a vector sorted into order with the largest first. The exception Constraint_Error is raised if A'Length(1) is not equal to A'Length(2). The index range of the result is A'Range(1).

procedure Values_And_Vectors(A : in Real_Matrix; Values : out Real_Vector; Vectors : out Real_Matrix);

This procedure computes both the eigenvalues and eigenvectors of the symmetric matrix A. The out parameter Values is the same as that obtained by calling the function Values. The out parameter Vectors is a matrix whose columns are the eigenvectors of the matrix A. The order of the columns corresponds to the order of the eigenvalues. The eigenvectors are normalized and mutually orthogonal (they are orthonormal),including when there are repeated eigenvalues. The exception Constraint_Error is raised if A'Length(1) is not equal to A'Length(2). The index ranges of the parameter Vectors are those of A.

For both subprograms, if the matrix A is not symmetric then Constraint_Error is raised.

?? Or we could define the matrix just in terms of the upper diagonal or we could make it symmetric by taking the arithmetic mean of the matrix and its transpose.

Eigenvalues and eigenvectors of a general real or complex matrix are computed using subprograms in the child package Ada.Numerics.Generic_Complex_Arrays.Eigen whose declaration is:

generic package Ada.Numerics.Generic_Complex_Arrays.Eigen is pragma Pure(Eigen);

-- Eigensystem of a general real matrix

function Values(A : Real_Matrix) return Complex_Vector;

procedure Values_And_Vectors(A : in Real_Matrix; Values : out Complex_Vector; Vectors : out Complex_Matrix);

-- Eigensystem of a Hermitian matrix

function Values(A : Complex_Matrix) return Real_Vector;

procedure Values_And_Vectors(A : in Complex_Matrix; Values : out Real_Vector; Vectors : out Complex_Matrix);

-- Eigensystem of a general complex matrix

function Values(A : Complex_Matrix) return Complex_Vector;

procedure Values_And_Vectors(A : in Complex_Matrix; Values : out Complex_Vector; Vectors : out Complex_Matrix);

end Ada.Numerics.Generic_Complex_Arrays.Eigen;

The library package Numerics.Complex_Arrays.Eigen is declared pure and defines the same subprograms as Numerics.Generic_Complex_Arrays.Eigen, except that the Real_Vector and Real_Matrix types exported by Numerics.Real_Arrays are systematically substituted for Real_Vector and Real_Matrix throughout. Nongeneric equivalents for each of the other predefined floating point types are defined similarly, with the names Numerics.Short_Complex_Arrays.Eigen, Numerics.Long_Complex_Arrays.Eigen, etc.

?? I didn't mention Real'Base, Complex etc because they are not used in the spec. Should I??

The effect of the subprograms is as described below.

function Values(A : Real_Matrix) return Complex_Vector;

This function returns the eigenvalues of the matrix A as a vector sorted by order of modulus with the largest first. The exception Constraint_Error is raised if A'Length(1) is not equal to A'Length(2). The index range of the result is A'Range(1).

procedure Values_And_Vectors(A : in Real_Matrix; Values : out Complex_Vector; Vectors : out Complex_Matrix);

This procedure computes both the eigenvalues and eigenvectors of the matrix A. The out parameter Values is the same as that obtained by calling the function Values. The out parameter Vectors is a matrix whose columns are the eigenvectors of the matrix A. The order of the columns corresponds to the order of the eigenvalues. The exception Constraint_Error is raised if A'Length(1) is not equal to A'Length(2). The index ranges of the parameter Vectors are those of A.

function Values(A : Complex_Matrix) return Real_Vector;

This function returns the eigenvalues of the hermitian matrix A as a vector sorted into order with the largest first. The exception Constraint_Error is raised if A'Length(1) is not equal to A'Length(2). The index range of the result is A'Range(1). The exception Constraint_Error is raised if the matrix is not hermitian.

procedure Values_And_Vectors(A : in Complex_Matrix; Values : out Real_Vector; Vectors : out Complex_Matrix);

This procedure computes both the eigenvalues and eigenvectors of the hermitian matrix A. The out parameter Values is the same as that obtained by calling the function Values. The out parameter Vectors is a matrix whose columns are the eigenvectors of the matrix A. The order of the columns corresponds to the order of the eigenvalues. The eigenvectors are mutually orthonormal, including when there are repeated eigenvalues. The exception Constraint_Error is raised if A'Length(1) is not equal to A'Length(2). The index ranges of the parameter Vectors are those of A. The exception Constraint_Error is raised if the matrix is not hermitian.

?? Or we could define the matrix just in terms of the upper diagonal or we could make it hermitian by taking the arithmetic mean of the matrix and its conjugate transpose.

function Values(A : Complex_Matrix) return Complex_Vector;

procedure Values_And_Vectors(A : in Complex_Matrix; Values : out Complex_Vector; Vectors : out Complex_Matrix);

Implementation Requirements

The accuracy of these subprograms is implementation defined.

Implementation Permissions

The nongeneric equivalent packages may, but need not, be actual instantiations of the generic package for the appropriate predefined type.

!example

To be done by someone else.

!discussion

The packages closely follow those in 13813. However, the discussion has been considerably simplified by assuming the properties of the corresponding scalar operations such as those in Numerics.Complex_Types. This removes a lot of explicit mention of raising exceptions and accuracy. Also remarks that these are standard mathematical operations have been deleted when the meaning is given by other words in the description.

The component by component operations of * / and ** on vectors have been deleted on the grounds that they are not useful. (They might be useful for manipulating arrays in general but we are concerned with arrays used as vectors for linear algebra.)

Operations for vector products have been added, However, this might be considered curious because they only apply in three-dimensional space.

?? And I put the inner outer and vector products together which might not have been a good idea.

It is hoped that there is not too much confusion between component when applied to the parts of a complex number and component when applied to a part of an array. 13813 uses element for the latter but the proper Ada term for an element of an array or field of a record is of course component.

Observe that the index range of the various arrays is Integer (rather than Natural or Positive). This permits negative indices and in particular arrays with symmetric index ranges about zero.

The function Identity_Matrix of 13813 has been changed to Unit_Matrix on the grounds that the prime concern is with linear algebra and not group theory.

Functions have been added to Numerics.Generic_Real_Arrays for matrix inversion and related operations. On the grounds that it would be helpful to have simple algorithms available to users rather than none at all, no accuracy requirements are specified. Instead the accuracy is stated to be implementation-defined which means that the implementation must document it.

The names chosen are Solve and Inverse. The former is overloaded, one version solves a single set of linear equations; the second solves multiple sets. Note that Inverse is not strictly necesssary becuase the effect can be obtained by using Solve and a Unit_Matrix thus

I := Unit_Matrix(A'Length); B := Solve(A, I); -- same as B := Inverse (A);

A function for computing the determinant has been added since it is helpful in deciding whether an array is ill-conditioned and therefore the results of inversion might be suspect.

Similar functions have also been added for complex arrays.

In addition, subprograms have been added for the computation of eigenvalues and vectors of real and complex arrays. Because these are somewhat more specialized than the elementary operations they have been placed in generic child packages such as Numerics.Generic_Real_Arrays.Eigen. The individual sunprograms are Values and Values_And_Vectors which means that they can be invoked by statements such as

V := Eigen.Values(A);

There is no separate function for eigenvectors since it is unlikely that these would be required without the eigenvalues.

The most common application is with real symmetric matrices and these have real eigenvalues and vectors. Hence the subprograms in the real package only cater for symmetric matrices. Applications include: moments of inertia, elasticity, confidence regions and so on.

A general real matrix can have complex eigenvalues and therefore provision for these and complex matrices is in the complex package. Note that the analogue of symmetric matrices in the complex domain is hermitian matrices (the transpose of a hermitian matrix equals its complex conjugate); these have real eigenvalues and distinct provision is made for these. The various overloadings are conveniently distinguished by the parameter profiles. (but could not be if there were separate fuinctions for the eigenvectors).

?? I am somewhat rusty on eigensystems of non-symmetric matrices. I have said nothing about the normalization of the vectors. Note that I put all the eigen stuff in 3.3 - that's partly so it can be removed easily!!

The original text of 13813 contains the remark "no complex conjugation is performed" in the description of multiplication of complex vectors to produce a complex matrix. I removed it because it seemed unhelpful to the user. The origin of this according to Donald Sando is that the NUMWG considered including various combined operations involving both multiplication and conjugation and indeed multiplication and transposition. Multiplication and conjugation are natural when dealing with for example Hermitian matrices. however, to provided all the appropriate combinations would have greatly increased the size of the package so it says in the rationale section F.3 of the 1998 version of 13813.

Terry Froggatt adds further thoughts on this matter (private communication, 17 July 2001. Thus

2. THOUGHTS ON TRANSPOSITION.

This comment arises from the last paragraph of F.3 of the Rationale in Annexe F ....

In the Harrier flight-program we have several spatial co-ordinate systems, for example:

Earth Axes: North - East - Up. Heading - Cross-heading - Up, (yawed wrt Earth). Aircraft Axes (rolled/pitched/yawed wrt Earth). HUD Axes (6 degrees down from Aircraft Axes).

Conversion of vectors between pairs of these systems uses matrix multiplication one way, and multiplication by the tranpose of the same matrix the other way.

Whilst X*CONJUGATE(Y) may be acceptable, since X and Y are the same size, the costs for X*TRANSPOSE(Y) are different: Y is generally much bigger than X, and it seems rather wasteful (mainly in time) to put the transpose of a matrix onto the stack then throw it away.

An alternative is to calculate T := TRANSPOSE(Y) as soon as Y is calculated, so that it is available to convert several vectors between a pair of axis systems. This is wasteful (mainly in space) because several transposes have to be kept around simultaneously.

What we actually use is one routine which implements X*TRANSPOSE(Y) directly: it performs the matrix multiplication but traverses Y in transpose-order. This takes no more time than the normal multiply, and no space for transposes (just code space).

This is exactly what 13813's rationale rejected.

Note that it should be possible to express the Harrier routine, and calls to it, quite neatly in Ada. Following the style of "Imaginary", define:

type Transposed_Real_Matrix is private; ... type Transposed_Real_Matrix is new Real_Matrix; function Transpose_In_Situ is new Unchecked_Conversion (Real_Matrix, Transposed_Real_Matrix);

function "*" (Left: Real_Vector; Right: Transposed_Real_Matrix)

return (Real_Vector);

This "*" knows it has to traverse Right in transposed order, and can be called (using operator notation, and no qualification) by

"Z := X*Transpose_In_Situ(Y);".

end of Remark by Terry Froggatt.

Well now. It seems to me that playing with Hermitian matrices is pretty rare and so we can forget about possible combinations of conjugate and multiply. However, maybe there is a case for adding some combined multiplication and transposition for the real matrices as explained above.

!ACATS Test

ACATS test(s) need to be created.

!appendix


****************************************************************

Recommendation on ISO/IEC 13813 from the UK

The standard ISO/IEC 13813 entitled generic packages of real and complex type
declarations and basic operations for Ada (including vector and matrix types)
will soon be up for review. This note reviews the background to the development
of the standard and makes a recommendation that the standard be revised.

Background

The Numerics Working Group of WG9 met many times during the period when Ada 95
was being designed and produced a number of standards. They were faced with the
problem of whether to produce standards based on Ada 83 (87 in ISO terms) or
whether to base them on Ada 95 or subsume them into Ada 95. One dilemma was of
course that although Ada 95 was on the way nevertheless Ada 83 was expected to
continue in use for many years.

The standards are
  11430: Generic package of elementary functions for Ada.
  11729: Generic package of primitive functions for Ada.
  13813: Generic packages of real and complex type declarations and basic
         operations for Ada (including vector and matrix types).
  13814: Generic package of complex elementary functions for Ada.

11430 and 11729 are mentioned for completeness. They were published in 1994.
They were based entirely on Ada 83 and their facilities are provided in the Ada
95 core language. The elementary functions, 11430, became the package
Ada.Numerics.Generic_Elementary_Functions and the primitive functions, 11729,
became the various attributes such as 'Floor and 'Ceiling, and 'Exponent and
'Fraction. These two standards were withdrawn recently and need no further
mention.

The other two standards, 13813 and 13814, were published in 1998 and will soon
be up for review at the end of their five year period. Three possible fates can
befall a standard when it is reviewed. It can be withdrawn, revised or
confirmed.

In the case of 13814, the functionality is all incorporated into the Numerics
Annex of Ada 95 as the package
Ada.Numerics.Generic_Complex_Elementary_Functions. There are a few changes in
presentation because the Ada 95 package uses the generic package parameter
feature which of course did not exist in Ada 83. Nevertheless there seems
little point in continuing with 13814 and so at the Leuven meeting of WG9 it
was agreed to recommend that it be withdrawn.

However, the situation regarding 13813 is not so clear. Some of its
functionality is included in Ada 95 but quite a lot is not. The topics covered
are (1) a complex types package including various complex arithmetic
operations, (2) a real arrays package covering both vectors and matrices, (3) a
complex arrays package covering  both vectors and matrices, (4) a complex
input-output package.

The complex types package (1) became the package
Ada.Numerics.Generic_Complex_Types and the input-output package (4) became
Ada.Text_IO.Complex_IO. However, the array packages, both real and complex,
were not incorporated into the Ada 95 standard.

At the Leuven meeting, it was agreed that 13813 should not be withdrawn without
further study. The UK was asked to study whether small or large changes are
required in 13813 and to report back. The Ada Rapporteur Group would then
decide whether the functionality should be included in a future revision or
amendment to Ada 95.

This is the report from the UK.

Recommendation

It is recommended that 13813 be revised so that it only contains the
functionality not included in Ada 95.

The revised standard should contain two generic packages namely
Ada.Numerics.Generic_Real_Arrays and Ada.Numerics.Generic_Complex_Arrays.

There should also be standard non-generic packages corresponding to the
predefined types such as Float in an analogous manner to the standard packages
such as Ada.Numerics.Complex_Types and Ada.Numerics.Long_Complex_Types for
Float and Long_Float respectively.

The text of the Ada specifications of the two generic packages should be
essentially as given in the nonnormative Annex G of the existing standard
13813. (This Annex illustrates how the existing standard packages might be
rewritten using Ada 95. There is an error regarding the formal package
parameters which has been corrected in the revised text.)

There is an important issue regarding what should happen if there is a mismatch
in the array lengths of the parameters in a number of the subprograms provided
by the packages. For example if

   function "+" (Left, Right: Real_Vector) return Real_Vector

be called with parameters such that Left'Length /= Right'Length.

The existing standard raises the exception Array_Index_Error which is declared
alone in a package Array_Exceptions. The nonnormative Annex G shows this
exception incorporated into the package Ada.Numerics thereby producing an
incompatibility with the existing definition of Ada.Numerics.

We considered four possibilities regarding this exception
  1) Add Array_Index_Error to Ada.Numerics as in Annex G.
  2) Place Array_Index_Error in a new child package such as Ada.Numerics.Arrays.
  3) Eliminate Array_Index_Error and raise Constraint_Error instead.
  4) State that the behaviour with mismatched arrays is implementation-defined.

We concluded that
  Option (1) is undesirable because of incompatibility.
  Option (2) is feasible but one ought then to place the generic packages
  themselves into this package so that they become
  Ada.Numerics.Arrays.Generic_Real_Arrays and
  Ada.Numerics.Arrays.Generic_Complex_Arrays. This nesting is considered
  cumbersome.
  Option(3) gives the same behaviour as similar mismatching on predefined
  operations and although losing some specificacity has practical simplicity.
  Option (4) is disliked since gratuitous implementation-defined
  behaviour should be avoided.

We therefore recommend Option (3) that Constraint_Error be raised on
mismatching of parameters.

If the Ada95 standard itself be revised at some later date then consideration
should be given to incorporating the functionality of the revised 13813 into
the Numerics Annex.

Proposed text

The proposed normative text of the revised standard is distributed separately
as N404, Working Draft, Revision of ISO/IEC 13813. Note that the non-normative
rationale section remains to be completed and that consequently the
bibliography might need alterations to match.

Acknowledgment

We acknowledge the valuable assistance of Donald Sando, the editor of the
original standard, in the preparation of this recommendation.

****************************************************************

From: John Barnes
Sent: Tuesday, January 21, 2003  10:33 AM

Gosh - I have made a start on AI-296. [Editor's note: This is version /01
of the AI.]

I have pulled all the Ada text in and written a first cut at
the description for the real vectors and matrices. I thought
maybe it would be a good idea to get the style settled
before spending time on the complex ones.

Here are some thoughts.

There are questions of how to arrange the annex in
!proposal.

What do we use for the plural of index when talking about
arrays?  I suspect that it ought to be indexes and not
indices as Don had.

I have slimmed down the accuracy and error stuff that Don
Sando had by simply referring to the underlying real
operations. There are as yet no useful remarks on the
accuracy of inner product.

I started by explaining the bounds of the result in terms of
the bounds of the parameters whereas Don had done it in
terms of ranges. Later I discovered that ranges are much
easier for the more elaborate matrix cases so perhaps I
should have used ranges throughout. Thus saying for example
"the index range of the result is Left'Range" rather than
"the bounds of the result are those of the left operand".

I am not sure whether I need to say anything about null
arrays. I note that 4.5.1(8) doesn't seem to.

Incidentally, I am still overwhelmed with other work.
Although the Spark book has gone away to be proof read, it
re-emerges tomorrow and will keep me busy for several days
in doing final corrections. Also I have to prepare a one-day
course on Spark at the University of York the week after
Padua so I have to send the notes beforehand. I do this
course each year but at the last minute they want a lot of
changes.

But we do have a baseline to discuss on AI-296 for Padua even
if I don't get a chance to spend much more time on it before
then. So I don't feel too guilty.

There is a lot of interest in this stuff (especially
problems of accuracy) in the UK and we have a BSI meeting in
mid February to discuss this.

****************************************************************

From: Pascal Leroy
Sent: Wednesday, January 22, 2003  8:24 AM

> There are as yet no useful remarks on the
> accuracy of inner product.

I think that the accuracy of the inner product should be defined in a way
similar to that of the complex multiplication.  If you look at the inner
product of vectors (a1, a2) and (b1, b2), the result is quite similar to the
real part of the (complex) multiplication of a1 + ib1 and a1 - ib2.

The box error in G.2.5 ensures that if the result of a multiplication lands
very close to one of the axis, you don't have to provide an unreasonable
accuracy on the "small" component, because presumably cancellations happened.
Moreover, the "large" component gives you some information on the magnitude of
the cancellation, so it can be used to define the acceptable error.  That's
essentially what the box error does (at least that's my understanding).

For the inner product of v1 and v2, I believe that the error should similarly
be defined to be of the form d * length(v1) * length (v2).  If cancellations
happen, i.e. if the vectors are nearly orthogonal, the error can be quite large
compared to the final result.  In the absence of cancellations, i.e. if the
vectors are not orthogonal, then with a proper choice for d we can require good
accuracy.

The alert reader will notice that this amounts to defining the relative error
on the result as d/cos (A) where A is the angle of the two vectors.

This is just a back-of-an-envelope proposal.  No rigorous analysis was done.

****************************************************************

From: John Barnes
Sent: Tuesday, June 10, 2003  4:42 AM

Vectors and matrices

At the last ARG meeting I was asked to add material for
matrix inversion, solution of linear equations,
determinants, and eigenvalues and vectors. We very briefly
considered a couple of other topics but dismissed them as
tricky.

I have updated AI-296 as instructed and sent it to Randy so
I assume it is now on the database. [Editor's note: This is
version /02 of the AI.]

I put the linear equations, invert and determinant in the
main packages (one for reals and one for complex). I put the
eigenvalues and vectors in child packages because they
seemed a bit different - also they were more complex than I
had remembered (I hadn't looked at this stuff for nearly
half a century) and maybe they are more elaborate than we
need.

There are a number of queries embedded in the text
concerning accuracy etc.

However, there are a number of other matters which ought to
be discussed. I visited NAG (National Algorithms Group).
They did a lot of Ada 83 numerics stuff once although they
no longer sell it. They did implement 13813.

They put the invert stuff in separate packages but it is
much more elaborate than my humble proposal. For example
they have options on whether to invert just once or to
iterate on the residuals until they are acceptable. But then
of course one has to give the accuracy required (although
they do have defaults). Moreover the LU decomposition is
made visible.

Now as a user, I don't really want to know about how it is
done (in a sense it breaks the abstraction), I just want the
answer. They have provided what the numerical analyst
specialist would want and I don't really think that is
appropriate for a simple standard but maybe I am wrong. Thus
their subprograms have some 10 parameters whereas in my
proposal they are the minimal one or two. For instance their
determinant has eight parameters whereas mine has one.

In the case of eigenvalues and vectors, they had options to
select just the largest or smallest or all those in a
certain range. No doubt because of timing considerations for
large matrices.

We also considered other topics which might provide
candidates for a standard.
The trouble with many topics is that techniques are still
evolving and it is unclear that a unique worthy proposal
would be easy.

Curve and surface fitting. There is lots of choice here.
Cubic splines are fashionable. Chebychev polynolmials are a
long established technique. But both require significant
user knowledge and it is easy to misuse them.

Maximization/minimization. Lots of options here and real
problems have constraints. The techniques are heuristic and
still evolving so this looks really hard and can be
eliminated.

Partial differential equations seem too much for the casual
user. In any event there is a huge variety of parameters and
constraints.

Ordinary differential equations and quadrature (integration)
are perhaps more promising. Again there are quite a lot of
options. But this might be worth exploring.

Roots of general non-linear equations. An evolving subject
still. Very heuristic and prone to chaotic difficulties.

Roots of polynomial equations. This seemed more likely . It
appears that the subject is static and a well-established
technique devised by Laguerre is typically used. (But it is
outside my domain of knowledge.)

I have also contemplated my 20 year old HP pocket
calculator. I had a vague feeling that Ada should be able to
do what it can do. It can do the following:

The usual trigonometric and hyperbolic functions.

Real and complex matrices, linear equations, inversion and
determinants (reveals the LU decomposition). It does not do
eigenvalues.

Random number generation. A whole heap of statistical stuff.

Integration (quadrature) of a function of one variable.

Solution of a non-linear equation in one variable.

So where do we go from here? It is a slippery slope and I
fear that I am not an expert.

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