strsm

STRSM(l)                         BLAS routine                         STRSM(l)



NAME
       STRSM - solve one of the matrix equations   op( A )*X = alpha*B, or
       X*op( A ) = alpha*B,

SYNOPSIS
       SUBROUTINE STRSM ( SIDE, UPLO, TRANSA, DIAG, M, N, ALPHA, A, LDA, B,
                        LDB )

           CHARACTER*1  SIDE, UPLO, TRANSA, DIAG

           INTEGER      M, N, LDA, LDB

           REAL         ALPHA

           REAL         A( LDA, * ), B( LDB, * )

PURPOSE
       STRSM  solves one of the matrix equations

       where alpha is a scalar, X and B are m by n matrices, A is a unit, or
       non-unit,  upper or lower triangular matrix  and  op( A )  is one  of

          op( A ) = A   or   op( A ) = A'.

       The matrix X is overwritten on B.


PARAMETERS
       SIDE   - CHARACTER*1.
              On entry, SIDE specifies whether op( A ) appears on the left or
              right of X as follows:

              SIDE = 'L' or 'l'   op( A )*X = alpha*B.

              SIDE = 'R' or 'r'   X*op( A ) = alpha*B.

              Unchanged on exit.

       UPLO   - CHARACTER*1.
              On entry, UPLO specifies whether the matrix A is an upper or
              lower triangular matrix as follows:

              UPLO = 'U' or 'u'   A is an upper triangular matrix.

              UPLO = 'L' or 'l'   A is a lower triangular matrix.

              Unchanged on exit.

              TRANSA - CHARACTER*1.  On entry, TRANSA specifies the form of
              op( A ) to be used in the matrix multiplication as follows:

              TRANSA = 'N' or 'n'   op( A ) = A.

              TRANSA = 'T' or 't'   op( A ) = A'.

              TRANSA = 'C' or 'c'   op( A ) = A'.

              Unchanged on exit.

       DIAG   - CHARACTER*1.
              On entry, DIAG specifies whether or not A is unit triangular as
              follows:

              DIAG = 'U' or 'u'   A is assumed to be unit triangular.

              DIAG = 'N' or 'n'   A is not assumed to be unit triangular.

              Unchanged on exit.

       M      - INTEGER.
              On entry, M specifies the number of rows of B. M must be at
              least zero.  Unchanged on exit.

       N      - INTEGER.
              On entry, N specifies the number of columns of B.  N must be at
              least zero.  Unchanged on exit.

       ALPHA  - REAL            .
              On entry,  ALPHA specifies the scalar  alpha. When  alpha is
              zero then  A is not referenced and  B need not be set before
              entry.  Unchanged on exit.

       A      - REAL             array of DIMENSION ( LDA, k ), where k is m
              when  SIDE = 'L' or 'l'  and is  n  when  SIDE = 'R' or 'r'.
              Before entry  with  UPLO = 'U' or 'u',  the  leading  k by k
              upper triangular part of the array  A must contain the upper
              triangular matrix  and the strictly lower triangular part of A
              is not referenced.  Before entry  with  UPLO = 'L' or 'l',  the
              leading  k by k lower triangular part of the array  A must
              contain the lower triangular matrix  and the strictly upper
              triangular part of A is not referenced.  Note that when  DIAG =
              'U' or 'u',  the diagonal elements of A  are not referenced
              either,  but are assumed to be  unity.  Unchanged on exit.

       LDA    - INTEGER.
              On entry, LDA specifies the first dimension of A as declared in
              the calling (sub) program.  When  SIDE = 'L' or 'l'  then LDA
              must be at least  max( 1, m ),  when  SIDE = 'R' or 'r' then LDA
              must be at least max( 1, n ).  Unchanged on exit.

       B      - REAL             array of DIMENSION ( LDB, n ).
              Before entry,  the leading  m by n part of the array  B must
              contain  the  right-hand  side  matrix  B,  and  on exit  is
              overwritten by the solution matrix  X.

       LDB    - INTEGER.
              On entry, LDB specifies the first dimension of B as declared in
              the  calling  (sub)  program.   LDB  must  be  at  least max( 1,
              m ).  Unchanged on exit.

              Level 3 Blas routine.

              -- Written on 8-February-1989.  Jack Dongarra, Argonne National
              Laboratory.  Iain Duff, AERE Harwell.  Jeremy Du Croz, Numerical
              Algorithms Group Ltd.  Sven Hammarling, Numerical Algorithms
              Group Ltd.







BLAS routine                    16 October 1992                       STRSM(l)