NAG Library Routine Document

F01CKF

1  Purpose

2  Specification

3  Description

4  References

5  Parameters

1:     A(N,P) – double precision arrayOutput

On exit: if OPT=1, A contains the result of the matrix multiplication.

2:     B(N,M) – double precision arrayInput/Output

On entry: the n by m matrix B.

On exit: if OPT=2, B contains the result of the multiplication.

3:     C(M,P) – double precision arrayInput/Output

On entry: the m by p matrix C.

On exit: if OPT=3, C contains the result of the multiplication.

4:     N – INTEGERInput

On entry: n, the number of rows of the array A and of the array B.

Constraints:

• if OPT=3, N=M;
• otherwise N≥1.

5:     P – INTEGERInput

On entry: p, the number of columns of the array A and of the array C.

Constraints:

• if OPT=2, P=M;
• otherwise P≥1.

6:     M – INTEGERInput

On entry: m, the number of columns of the array B and rows of the array C.

Constraints:

• if OPT=2, M=P;
• if OPT=3, M=N;
• if OPT≠1, M≤IZ;
• otherwise M≥1.

7:     Z(IZ) – double precision arrayWorkspace

8:     IZ – INTEGERInput

On entry: the dimension of the array Z as declared in the (sub)program from which F01CKF is called.

Constraints:

• if OPT=1, IZ≥1;
• if OPT≠1, IZ≥M.

9:     OPT – INTEGERInput

On entry: the value of OPT determines which array is to contain the final result.

OPT=1

A must be distinct from B and C and, on exit, contains the result. B and C need not be distinct in this case.

OPT=2

B must be distinct from C and on exit, contains the result. A is not used in this case and need not be distinct from B or C.

OPT=3

C must be distinct from B and on exit, contains the result. A is not used in this case and need not be distinct from B or C.

Constraint: 1≤OPT≤3.

10:   IFAIL – INTEGERInput/Output

On entry: IFAIL must be set to 0, -1​ or ​1. If you are unfamiliar with this parameter you should refer to Section 3.3 in the Essential Introduction for details.

On exit: IFAIL=0 unless the routine detects an error (see Section 6).

For environments where it might be inappropriate to halt program execution when an error is detected, the value -1​ or ​1 is recommended. If the output of error messages is undesirable, then the value 1 is recommended. Otherwise, if you are not familiar with this parameter, the recommended value is 0. When the value -1​ or ​1 is used it is essential to test the value of IFAIL on exit.

6  Error Indicators and Warnings

IFAIL=1

On entry, M or P or N≤0.

IFAIL=2

OPT=2 and M≠P.

IFAIL=3

OPT=3 and N≠M.

IFAIL=4

OPT≠1 and IZ<M.

7  Accuracy

8  Further Comments

9  Example

9.1  Program Text

Program Text (f01ckfe.f)

9.2  Program Data

9.3  Program Results

Program Results (f01ckfe.r)