NAG FL Interfacef06yaf (dgemm)

1Purpose

f06yaf performs one of the matrix-matrix operations
 $C←αAB+βC, C←αATB+βC, C←αABT+βC or C←αATBT+βC,$
where $A$, $B$ and $C$ are real matrices, and $\alpha$ and $\beta$ are real scalars; $C$ is always $m$ by $n$.

2Specification

Fortran Interface
 Subroutine f06yaf ( m, n, k, a, lda, b, ldb, beta, c, ldc)
 Integer, Intent (In) :: m, n, k, lda, ldb, ldc Real (Kind=nag_wp), Intent (In) :: alpha, a(lda,*), b(ldb,*), beta Real (Kind=nag_wp), Intent (Inout) :: c(ldc,*) Character (1), Intent (In) :: transa, transb
#include <nag.h>
 void f06yaf_ (const char *transa, const char *transb, const Integer *m, const Integer *n, const Integer *k, const double *alpha, const double a[], const Integer *lda, const double b[], const Integer *ldb, const double *beta, double c[], const Integer *ldc, const Charlen length_transa, const Charlen length_transb)
The routine may be called by the names f06yaf, nagf_blas_dgemm or its BLAS name dgemm.

None.

None.

5Arguments

1: $\mathbf{transa}$Character(1) Input
On entry: specifies whether the operation involves $A$ or ${A}^{\mathrm{T}}$.
${\mathbf{transa}}=\text{'N'}$
The operation involves $A$.
${\mathbf{transa}}=\text{'T'}$ or $\text{'C'}$
The operation involves ${A}^{\mathrm{T}}$.
Constraint: ${\mathbf{transa}}=\text{'N'}$, $\text{'T'}$ or $\text{'C'}$.
2: $\mathbf{transb}$Character(1) Input
On entry: specifies whether the operation involves $B$ or ${B}^{\mathrm{T}}$.
${\mathbf{transb}}=\text{'N'}$
The operation involves $B$.
${\mathbf{transb}}=\text{'T'}$ or $\text{'C'}$
The operation involves ${B}^{\mathrm{T}}$.
Constraint: ${\mathbf{transb}}=\text{'N'}$, $\text{'T'}$ or $\text{'C'}$.
3: $\mathbf{m}$Integer Input
On entry: $m$, the number of rows of the matrix $C$; the number of rows of $A$ if ${\mathbf{transa}}=\text{'N'}$, or the number of columns of $A$ if ${\mathbf{transa}}=\text{'T'}$ or $\text{'C'}$.
Constraint: ${\mathbf{m}}\ge 0$.
4: $\mathbf{n}$Integer Input
On entry: $n$, the number of columns of the matrix $C$; the number of columns of $B$ if ${\mathbf{transb}}=\text{'N'}$, or the number of rows of $B$ if ${\mathbf{transb}}=\text{'T'}$ or $\text{'C'}$.
Constraint: ${\mathbf{n}}\ge 0$.
5: $\mathbf{k}$Integer Input
On entry: $k$, the number of columns of $A$ if ${\mathbf{transa}}=\text{'N'}$, or the number of rows of $A$ if ${\mathbf{transa}}=\text{'T'}$ or $\text{'C'}$; the number of rows of $B$ if ${\mathbf{transb}}=\text{'N'}$, or the number of columns of $B$ if ${\mathbf{transb}}=\text{'T'}$ or $\text{'C'}$.
Constraint: ${\mathbf{k}}\ge 0$.
6: $\mathbf{alpha}$Real (Kind=nag_wp) Input
On entry: the scalar $\alpha$.
7: $\mathbf{a}\left({\mathbf{lda}},*\right)$Real (Kind=nag_wp) array Input
Note: the second dimension of the array a must be at least $\mathrm{max}\phantom{\rule{0.125em}{0ex}}\left(1,{\mathbf{k}}\right)$ if ${\mathbf{transa}}=\text{'N'}$ and at least $\mathrm{max}\phantom{\rule{0.125em}{0ex}}\left(1,{\mathbf{m}}\right)$ if ${\mathbf{transa}}=\text{'T'}$ or $\text{'C'}$.
On entry: the matrix $A$; $A$ is $m$ by $k$ if ${\mathbf{transa}}=\text{'N'}$, or $k$ by $m$ if ${\mathbf{transa}}=\text{'T'}$ or $\text{'C'}$.
8: $\mathbf{lda}$Integer Input
On entry: the first dimension of the array a as declared in the (sub)program from which f06yaf is called.
Constraints:
• if ${\mathbf{transa}}=\text{'N'}$, ${\mathbf{lda}}\ge \mathrm{max}\phantom{\rule{0.125em}{0ex}}\left(1,{\mathbf{m}}\right)$;
• if ${\mathbf{transa}}=\text{'T'}$ or $\text{'C'}$, ${\mathbf{lda}}\ge \mathrm{max}\phantom{\rule{0.125em}{0ex}}\left(1,{\mathbf{k}}\right)$.
9: $\mathbf{b}\left({\mathbf{ldb}},*\right)$Real (Kind=nag_wp) array Input
Note: the second dimension of the array b must be at least $\mathrm{max}\phantom{\rule{0.125em}{0ex}}\left(1,{\mathbf{n}}\right)$ if ${\mathbf{transb}}=\text{'N'}$ and at least $\mathrm{max}\phantom{\rule{0.125em}{0ex}}\left(1,{\mathbf{k}}\right)$ if ${\mathbf{transb}}=\text{'T'}$ or $\text{'C'}$.
On entry: the matrix $B$; $B$ is $k$ by $n$ if ${\mathbf{transb}}=\text{'N'}$, or $n$ by $k$ if ${\mathbf{transb}}=\text{'T'}$ or $\text{'C'}$.
10: $\mathbf{ldb}$Integer Input
On entry: the first dimension of the array b as declared in the (sub)program from which f06yaf is called.
Constraints:
• if ${\mathbf{transb}}=\text{'N'}$, ${\mathbf{ldb}}\ge \mathrm{max}\phantom{\rule{0.125em}{0ex}}\left(1,{\mathbf{k}}\right)$;
• if ${\mathbf{transb}}=\text{'T'}$ or $\text{'C'}$, ${\mathbf{ldb}}\ge \mathrm{max}\phantom{\rule{0.125em}{0ex}}\left(1,{\mathbf{n}}\right)$.
11: $\mathbf{beta}$Real (Kind=nag_wp) Input
On entry: the scalar $\beta$.
12: $\mathbf{c}\left({\mathbf{ldc}},*\right)$Real (Kind=nag_wp) array Input/Output
Note: the second dimension of the array c must be at least $\mathrm{max}\phantom{\rule{0.125em}{0ex}}\left(1,{\mathbf{n}}\right)$.
On entry: the $m$ by $n$ matrix $C$.
If ${\mathbf{beta}}=0$, c need not be set.
On exit: the updated matrix $C$.
13: $\mathbf{ldc}$Integer Input
On entry: the first dimension of the array c as declared in the (sub)program from which f06yaf is called.
Constraint: ${\mathbf{ldc}}\ge \mathrm{max}\phantom{\rule{0.125em}{0ex}}\left(1,{\mathbf{m}}\right)$.

None.

Not applicable.

8Parallelism and Performance

f06yaf 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.