NAG Library Routine Document

Integer, Intent (In)	::	m, n, lda, ldb, ldc
Integer, Intent (Inout)	::	ifail
Real (Kind=nag_wp), Intent (In)	::	alpha, a(lda,), beta, b(ldb,)
Real (Kind=nag_wp), Intent (Inout)	::	c(ldc,*)
Character (1), Intent (In)	::	transa, transb

C Header Interface

#include <nagmk26.h>

void

f01ctf_ (const char *transa, const char *transb, const Integer *m, const Integer *n, const double *alpha, const double a[], const Integer *lda, const double *beta, const double b[], const Integer *ldb, double c[], const Integer *ldc, Integer *ifail, const Charlen length_transa, const Charlen length_transb)

3

Description

f01ctf performs one of the operations

$C ≔ α A + β B$ ,
$C ≔ α A^{T} + β B$ ,
$C ≔ α A + β B^{T}$ or
$C ≔ α A^{T} + β B^{T}$ ,

where

A

B

and

C

are matrices, and

α

and

β

are scalars. For efficiency, the routine contains special code for the cases when one or both of

α

β

is equal to zero, unity or minus unity. The matrices, or their transposes, must be compatible for addition.

A

and

B

are either

m

n

n

m

matrices, depending on whether they are to be transposed before addition.

C

is an

m

n

matrix.

4

References

None.

5

Arguments

1: $transa$ – Character(1)Input

2: $transb$ – Character(1)Input

On entry: transa and transb must specify whether or not the matrix

A

and the matrix

B

, respectively, are to be transposed before addition.

transa or $transb ='N'$: The matrix will not be transposed.
transa or $transb ='T'$ or $'C'$: The matrix will be transposed.

Constraint:

transa ​ or ​ transb ='N'

'T'

'C'

3: $m$ – IntegerInput

On entry:

m

, the number of rows of the matrices

A

and

B

or their transposes. Also the number of rows of the matrix

C

Constraint:

m \geq 0

4: $n$ – IntegerInput

On entry:

n

, the number of columns of the matrices

A

and

B

or their transposes. Also the number of columns of the matrix

C

Constraint:

n \geq 0

5: $alpha$ – Real (Kind=nag_wp)Input

On entry: the scalar

α

, by which matrix

A

is multiplied before addition.

6: $a (lda *)$ – Real (Kind=nag_wp) arrayInput

Note: the second dimension of the array a must be at least

\max (1, n)

transa ='N'

, and at least

\max (1, m)

otherwise.

On entry: if

α = 0.0

, the elements of array a need not be assigned. If

α \neq 0.0

, then if

transa ='N'

, the leading

m

n

part of a must contain the matrix

A

, otherwise the leading

n

m

part of a must contain the matrix

A

7: $lda$ – IntegerInput

On entry: the first dimension of the array a as declared in the (sub)program from which f01ctf is called.

Constraints:

if $transa ='N'$ , $lda \geq \max (1, m)$ ;
otherwise $lda \geq \max (1, n)$ .

8: $beta$ – Real (Kind=nag_wp)Input

On entry: the scalar

β

, by which matrix

B

is multiplied before addition.

9: $b (ldb *)$ – Real (Kind=nag_wp) arrayInput

Note: the second dimension of the array b must be at least

\max (1, n)

transb ='N'

, and at least

\max (1, m)

otherwise.

On entry: if

β = 0.0

, the elements of array b need not be assigned. If

β \neq 0.0

, then if

transa ='N'

, the leading

m

n

part of b must contain the matrix

B

, otherwise the leading

n

m

part of b must contain the matrix

B

10: $ldb$ – IntegerInput

On entry: the first dimension of the array b as declared in the (sub)program from which f01ctf is called.

Constraints:

if $transb ='N'$ , $ldb \geq \max (1, m)$ ;
otherwise $ldb \geq \max (1, n)$ .

11: $c (ldc *)$ – Real (Kind=nag_wp) arrayOutput

Note: the second dimension of the array c must be at least

\max (1, n)

On exit: the elements of the

m

n

matrix

C

12: $ldc$ – IntegerInput

On entry: the first dimension of the array c as declared in the (sub)program from which f01ctf is called.

Constraint:

ldc \geq \max (1, m)

13: $ifail$ – IntegerInput/Output

On entry: ifail must be set to

0

- 1 or 1

. If you are unfamiliar with this argument you should refer to Section 3.4 in How to Use the NAG Library and its Documentation for details.

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 argument, the recommended value is

0

. When the value $- 1 or 1$ is used it is essential to test the value of ifail on exit.

On exit:

ifail = 0

unless the routine detects an error or a warning has been flagged (see Section 6).

6

Error Indicators and Warnings

If on entry

ifail = 0

- 1

, explanatory error messages are output on the current error message unit (as defined by x04aaf).

Errors or warnings detected by the routine:

$ifail = 1$: On entry, $transa = 〈value〉$ .
Constraint: $transa ='N'$ , $'T'$ or $'C'$ .

On entry, $transb = 〈value〉$ .
Constraint: $transb ='N'$ , $'T'$ or $'C'$ .

$ifail = 2$: On entry, $m = 〈value〉$ and $n = 〈value〉$ .
Constraint: $m \geq 0$ and $n \geq 0$ .

$ifail = 3$: On entry, $lda = 〈value〉$ and $m = 〈value〉$ .
Constraint: if $transa = 〈value〉$ , $lda \geq \max (1, m)$ .

On entry, $lda = 〈value〉$ and $n = 〈value〉$ .
Constraint: if $transa = 〈value〉$ , $lda \geq \max (1, n)$ .

$ifail = 4$: On entry, $ldb = 〈value〉$ and $m = 〈value〉$ .
Constraint: if $transb = 〈value〉$ , $ldb \geq \max (1, m)$ .

On entry, $ldb = 〈value〉$ and $n = 〈value〉$ .
Constraint: if $transb = 〈value〉$ , $ldb \geq \max (1, n)$ .

$ifail = 5$: On entry, $ldc = 〈value〉$ and $m = 〈value〉$ .
Constraint: $ldc \geq \max (1, m)$ .

$ifail = - 99$: An unexpected error has been triggered by this routine. Please contact NAG.
See Section 3.9 in How to Use the NAG Library and its Documentation for further information.

$ifail = - 399$: Your licence key may have expired or may not have been installed correctly.
See Section 3.8 in How to Use the NAG Library and its Documentation for further information.

$ifail = - 999$: Dynamic memory allocation failed.
See Section 3.7 in How to Use the NAG Library and its Documentation for further information.

7

Accuracy

The results returned by f01ctf are accurate to machine precision.

8

Parallelism and Performance

f01ctf is threaded by NAG for parallel execution in multithreaded implementations of the NAG Library.

Please consult the X06 Chapter Introduction for information on how to control and interrogate the OpenMP environment used within this routine. Please also consult the Users' Note for your implementation for any additional implementation-specific information.

9

Further Comments

The time taken for a call of f01ctf varies with m, n and the values of

α

and

β

. The routine is quickest if either or both of

α

and

β

are equal to zero, or plus or minus unity.

10

Example

The following program reads in a pair of matrices

A

and

B

, along with values for transa, transb, alpha and beta, and adds them together, printing the result matrix

C

. The process is continued until the end of the input stream is reached.

NAG Library Routine Document

f01ctf (real_addsub)

▸▿ Contents

1 Purpose

2 Specification

3 Description

4 References

5 Arguments

6 Error Indicators and Warnings

7 Accuracy

8 Parallelism and Performance

9 Further Comments

10 Example

10.1 Program Text

10.2 Program Data

10.3 Program Results

1

Purpose

2

Specification

3

Description

4

References

5

Arguments

6

Error Indicators and Warnings

7

Accuracy

8

Parallelism and Performance

9

Further Comments

10

Example

10.1

Program Text

10.2

Program Data

10.3

Program Results