HPL_dtrsm(3)

NAME
HPL_dtrsm - B := A^{-1} * B or B := B * A^{-1}.

SYNOPSIS
#include "hpl.h"

void HPL_dtrsm( const enum HPL_ORDER ORDER, const enum HPL_SIDE SIDE, const enum HPL_UPLO UPLO, const enum HPL_TRANS TRANS, const enum HPL_DIAG DIAG, const int M, const int N, const double ALPHA, const double * A, const int LDA, double * B, const int LDB );

DESCRIPTION
HPL_dtrsm solves one of the matrix equations

   op( A ) * X = alpha * B, or X * op( A ) = alpha * B,

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^T.

The matrix X is overwritten on B.

No test for singularity or near-singularity is included in this routine. Such tests must be performed before calling this routine.

ARGUMENTS

ORDER   (local input)           const enum HPL_ORDER
    On entry, ORDER specifies the storage format of the operands as follows:
       ORDER = HplRowMajor,
       ORDER = HplColumnMajor.

SIDE    (local input)           const enum HPL_SIDE
    On entry, SIDE specifies whether op(A) appears on the left or right of X as follows:
       SIDE==HplLeft op( A ) * X = alpha * B,
       SIDE==HplRight X * op( A ) = alpha * B.

UPLO    (local input)           const enum HPL_UPLO
    On entry, UPLO specifies whether the upper or lower triangular part of the array A is to be referenced. When UPLO==HplUpper, only the upper triangular part of A is to be referenced, otherwise only the lower triangular part of A is to be referenced.

TRANS   (local input)           const enum HPL_TRANS
    On entry, TRANSA specifies the form of op(A) to be used in the matrix-matrix operation follows:
       TRANSA==HplNoTrans : op( A ) = A,
       TRANSA==HplTrans : op( A ) = A^T,
       TRANSA==HplConjTrans : op( A ) = A^T.

DIAG    (local input)           const enum HPL_DIAG
    On entry, DIAG specifies whether A is unit triangular or not. When DIAG==HplUnit, A is assumed to be unit triangular, and otherwise, A is not assumed to be unit triangular.

M       (local input)           const int
    On entry, M specifies the number of rows of the matrix B. M must be at least zero.

N       (local input)           const int
    On entry, N specifies the number of columns of the matrix B. N must be at least zero.

ALPHA   (local input)           const double
    On entry, ALPHA specifies the scalar alpha. When ALPHA is supplied as zero then the elements of the matrix B need not be set on input.

A       (local input)           const double *
    On entry, A points to an array of size equal to or greater than LDA * k, where k is m when SIDE==HplLeft and is n otherwise. Before entry with UPLO==HplUpper, 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. When UPLO==HplLower on entry, 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==HplUnit, the diagonal elements of A not referenced either, but are assumed to be unity.

LDA     (local input)           const int
    On entry, LDA specifies the leading dimension of A as declared in the calling (sub) program. LDA must be at least MAX(1,m) when SIDE==HplLeft, and MAX(1,n) otherwise.

B       (local input/output)    double *
    On entry, B points to an array of size equal to or greater than LDB * n. Before entry, the leading m by n part of the array B must contain the matrix B, except when beta is zero, in which case B need not be set on entry. On exit, the array B is overwritten by the m by n solution matrix.

LDB     (local input)           const int
    On entry, LDB specifies the leading dimension of B as declared in the calling (sub) program. LDB must be at least MAX(1,m).

EXAMPLE
#include "hpl.h"

int main(int argc, char *argv[])
{
   double a[2*2], b[2*2];
   a[0] = 4.0; a[1] = 1.0; a[2] = 2.0; a[3] = 5.0;
   b[0] = 2.0; b[1] = 1.0; b[2] = 1.0; b[3] = 2.0;
   HPL_dtrsm( HplColumnMajor, HplLeft, HplUpper,
              HplNoTrans, HplNonUnit, 2, 2, 2.0,
              a, 2, b, 2 );
   printf(" [%f,%f]\n", b[0], b[2]);
   printf("b=[%f,%f]\n", b[1], b[3]);
   exit(0); return(0);
}

SEE ALSO
HPL_dgemm (3).