## MB01RW

### Computation of matrix expression alpha A X trans(A), X symmetric (BLAS 2 version)

[Specification] [Arguments] [Method] [References] [Comments] [Example]

Purpose

```  To compute the transformation of the symmetric matrix A by the
matrix Z in the form

A := op(Z)*A*op(Z)',

where op(Z) is either Z or its transpose, Z'.

```
Specification
```      SUBROUTINE MB01RW( UPLO, TRANS, M, N, A, LDA, Z, LDZ, DWORK,
\$                   INFO )
C     .. Scalar Arguments ..
CHARACTER         TRANS, UPLO
INTEGER           INFO, LDA, LDZ, M, N
C     .. Array Arguments ..
DOUBLE PRECISION  A(LDA,*), DWORK(*), Z(LDZ,*)

```
Arguments

Mode Parameters

```  UPLO    CHARACTER*1
Specifies whether the upper or lower triangle of A
is stored:
= 'U':  Upper triangle of A is stored;
= 'L':  Lower triangle of A is stored.

TRANS   CHARACTER*1
Specifies whether op(Z) is Z or its transpose Z':
= 'N':  op(Z) = Z;
= 'T':  op(Z) = Z'.

```
Input/Output Parameters
```  M       (input) INTEGER
The order of the resulting symmetric matrix op(Z)*A*op(Z)'
and the number of rows of the matrix Z, if TRANS = 'N',
or the number of columns of the matrix Z, if TRANS = 'T'.
M >= 0.

N       (input) INTEGER
The order of the symmetric matrix A and the number of
columns of the matrix Z, if TRANS = 'N', or the number of
rows of the matrix Z, if TRANS = 'T'.  N >= 0.

A       (input/output) DOUBLE PRECISION array, dimension
(LDA,MAX(M,N))
On entry, the leading N-by-N upper or lower triangular
part of this array must contain the upper (UPLO = 'U')
or lower (UPLO = 'L') triangular part of the symmetric
matrix A.
On exit, the leading M-by-M upper or lower triangular
part of this array contains the upper (UPLO = 'U') or
lower (UPLO = 'L') triangular part of the symmetric
matrix op(Z)*A*op(Z)'.

LDA     INTEGER
The leading dimension of the array A.  LDA >= MAX(1,M,N).

Z       (input) DOUBLE PRECISION array, dimension (LDQ,K)
where K = N if TRANS = 'N' and K = M if TRANS = 'T'.
The leading M-by-N part, if TRANS = 'N', or N-by-M part,
if TRANS = 'T', of this array contains the matrix Z.

LDZ     INTEGER
The leading dimension of the array Z.
LDZ >= MAX(1,M) if TRANS = 'N' and
LDZ >= MAX(1,N) if TRANS = 'T'.

```
Workspace
```  DWORK   DOUBLE PRECISION array, dimension (N)

```
Error Indicator
```  INFO    INTEGER
= 0:  successful exit;
< 0:  if INFO = -i, the i-th argument had an illegal
value.

```
```  This is a simpler, BLAS 2 version for MB01RD.

```
Example

Program Text

```  None
```
Program Data
```  None
```
Program Results
```  None
```