NAG Library Routine Document

f06zjf  (ztrsm)

 Contents

    1  Purpose
    7  Accuracy
    10  Example

1
Purpose

f06zjf (ztrsm) performs one of the matrix-matrix operations
BαA-1B , BαA-TB , BαA-HB , BαBA-1 , BαBA-T   or BαBA-H ,  
where A is a complex triangular matrix, B is an m by n complex matrix, and α is a complex scalar. A-T  denotes AT-1  or equivalently A-1T ; A-H  denotes AH-1  or equivalently A-1H .
No test for singularity or near-singularity of A is included in this routine. Such tests must be performed before calling this routine.

2
Specification

Fortran Interface
Subroutine f06zjf ( side, uplo, transa, diag, m, n, alpha, a, lda, b, ldb)
Integer, Intent (In):: m, n, lda, ldb
Complex (Kind=nag_wp), Intent (In):: alpha, a(lda,*)
Complex (Kind=nag_wp), Intent (Inout):: b(ldb,*)
Character (1), Intent (In):: side, uplo, transa, diag
C Header Interface
#include nagmk26.h
void  f06zjf_ ( const char *side, const char *uplo, const char *transa, const char *diag, const Integer *m, const Integer *n, const Complex *alpha, const Complex a[], const Integer *lda, Complex b[], const Integer *ldb, const Charlen length_side, const Charlen length_uplo, const Charlen length_transa, const Charlen length_diag)
The routine may be called by its BLAS name ztrsm.

3
Description

None.

4
References

None.

5
Arguments

1:     side – Character(1)Input
On entry: specifies whether B is operated on from the left or the right.
side='L'
B is pre-multiplied from the left.
side='R'
B is post-multiplied from the right.
Constraint: side='L' or 'R'.
2:     uplo – Character(1)Input
On entry: specifies whether A is upper or lower triangular.
uplo='U'
A is upper triangular.
uplo='L'
A is lower triangular.
Constraint: uplo='U' or 'L'.
3:     transa – Character(1)Input
On entry: specifies whether the operation involves A-1, A-T or A-H.
transa='N'
The operation involves A-1.
transa='T'
The operation involves A-T.
transa='C'
The operation involves A-H.
Constraint: transa='N', 'T' or 'C'.
4:     diag – Character(1)Input
On entry: specifies whether A has nonunit or unit diagonal elements.
diag='N'
The diagonal elements are stored explicitly.
diag='U'
The diagonal elements are assumed to be 1, and are not referenced.
Constraint: diag='N' or 'U'.
5:     m – IntegerInput
On entry: m, the number of rows of the matrix B; the order of A if side='L'.
Constraint: m0.
6:     n – IntegerInput
On entry: n, the number of columns of the matrix B; the order of A if side='R'.
Constraint: n0.
7:     alpha – Complex (Kind=nag_wp)Input
On entry: the scalar α.
8:     alda* – Complex (Kind=nag_wp) arrayInput
Note: the second dimension of the array a must be at least max1,m if side='L' and at least max1,n if side='R'.
On entry: the triangular matrix A; A is m by m if side='L', or n by n if side='R'.
  • If uplo='U', A is upper triangular and the elements of the array below the diagonal are not referenced.
  • If uplo='L', A is lower triangular and the elements of the array above the diagonal are not referenced.
  • If diag='U', the diagonal elements of A are assumed to be 1, and are not referenced.
9:     lda – IntegerInput
On entry: the first dimension of the array a as declared in the (sub)program from which f06zjf (ztrsm) is called.
Constraints:
  • if side='L', lda max1,m ;
  • if side='R', lda max1,n .
10:   bldb* – Complex (Kind=nag_wp) arrayInput/Output
Note: the second dimension of the array b must be at least max1,n.
On entry: the m by n matrix B.
If alpha=0, b need not be set.
On exit: the updated matrix B.
11:   ldb – IntegerInput
On entry: the first dimension of the array b as declared in the (sub)program from which f06zjf (ztrsm) is called.
Constraint: ldb max1,m .

6
Error Indicators and Warnings

None.

7
Accuracy

Not applicable.

8
Parallelism and Performance

f06zjf (ztrsm) 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

None.

10
Example

None.
© The Numerical Algorithms Group Ltd, Oxford, UK. 2017