sgetrs.c

Go to the documentation of this file.

/* sgetrs.f -- translated by f2c (version 20061008).
   You must link the resulting object file with libf2c:
        on Microsoft Windows system, link with libf2c.lib;
        on Linux or Unix systems, link with .../path/to/libf2c.a -lm
        or, if you install libf2c.a in a standard place, with -lf2c -lm
        -- in that order, at the end of the command line, as in
                cc *.o -lf2c -lm
        Source for libf2c is in /netlib/f2c/libf2c.zip, e.g.,

                http://www.netlib.org/f2c/libf2c.zip
*/

#include "f2c.h"
#include "blaswrap.h"

/* Table of constant values */

static integer c__1 = 1;
static real c_b12 = 1.f;
static integer c_n1 = -1;

/* Subroutine */ int sgetrs_(char *trans, integer *n, integer *nrhs, real *a, 
        integer *lda, integer *ipiv, real *b, integer *ldb, integer *info)
{
    /* System generated locals */
    integer a_dim1, a_offset, b_dim1, b_offset, i__1;

    /* Local variables */
    extern logical lsame_(char *, char *);
    extern /* Subroutine */ int strsm_(char *, char *, char *, char *, 
            integer *, integer *, real *, real *, integer *, real *, integer *
), xerbla_(char *, integer *);
    logical notran;
    extern /* Subroutine */ int slaswp_(integer *, real *, integer *, integer 
            *, integer *, integer *, integer *);


/*  -- LAPACK routine (version 3.2) -- */
/*     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. */
/*     November 2006 */

/*     .. Scalar Arguments .. */
/*     .. */
/*     .. Array Arguments .. */
/*     .. */

/*  Purpose */
/*  ======= */

/*  SGETRS solves a system of linear equations */
/*     A * X = B  or  A' * X = B */
/*  with a general N-by-N matrix A using the LU factorization computed */
/*  by SGETRF. */

/*  Arguments */
/*  ========= */

/*  TRANS   (input) CHARACTER*1 */
/*          Specifies the form of the system of equations: */
/*          = 'N':  A * X = B  (No transpose) */
/*          = 'T':  A'* X = B  (Transpose) */
/*          = 'C':  A'* X = B  (Conjugate transpose = Transpose) */

/*  N       (input) INTEGER */
/*          The order of the matrix A.  N >= 0. */

/*  NRHS    (input) INTEGER */
/*          The number of right hand sides, i.e., the number of columns */
/*          of the matrix B.  NRHS >= 0. */

/*  A       (input) REAL array, dimension (LDA,N) */
/*          The factors L and U from the factorization A = P*L*U */
/*          as computed by SGETRF. */

/*  LDA     (input) INTEGER */
/*          The leading dimension of the array A.  LDA >= max(1,N). */

/*  IPIV    (input) INTEGER array, dimension (N) */
/*          The pivot indices from SGETRF; for 1<=i<=N, row i of the */
/*          matrix was interchanged with row IPIV(i). */

/*  B       (input/output) REAL array, dimension (LDB,NRHS) */
/*          On entry, the right hand side matrix B. */
/*          On exit, the solution matrix X. */

/*  LDB     (input) INTEGER */
/*          The leading dimension of the array B.  LDB >= max(1,N). */

/*  INFO    (output) INTEGER */
/*          = 0:  successful exit */
/*          < 0:  if INFO = -i, the i-th argument had an illegal value */

/*  ===================================================================== */

/*     .. Parameters .. */
/*     .. */
/*     .. Local Scalars .. */
/*     .. */
/*     .. External Functions .. */
/*     .. */
/*     .. External Subroutines .. */
/*     .. */
/*     .. Intrinsic Functions .. */
/*     .. */
/*     .. Executable Statements .. */

/*     Test the input parameters. */

    /* Parameter adjustments */
    a_dim1 = *lda;
    a_offset = 1 + a_dim1;
    a -= a_offset;
    --ipiv;
    b_dim1 = *ldb;
    b_offset = 1 + b_dim1;
    b -= b_offset;

    /* Function Body */
    *info = 0;
    notran = lsame_(trans, "N");
    if (! notran && ! lsame_(trans, "T") && ! lsame_(
            trans, "C")) {
        *info = -1;
    } else if (*n < 0) {
        *info = -2;
    } else if (*nrhs < 0) {
        *info = -3;
    } else if (*lda < max(1,*n)) {
        *info = -5;
    } else if (*ldb < max(1,*n)) {
        *info = -8;
    }
    if (*info != 0) {
        i__1 = -(*info);
        xerbla_("SGETRS", &i__1);
        return 0;
    }

/*     Quick return if possible */

    if (*n == 0 || *nrhs == 0) {
        return 0;
    }

    if (notran) {

/*        Solve A * X = B. */

/*        Apply row interchanges to the right hand sides. */

        slaswp_(nrhs, &b[b_offset], ldb, &c__1, n, &ipiv[1], &c__1);

/*        Solve L*X = B, overwriting B with X. */

        strsm_("Left", "Lower", "No transpose", "Unit", n, nrhs, &c_b12, &a[
                a_offset], lda, &b[b_offset], ldb);

/*        Solve U*X = B, overwriting B with X. */

        strsm_("Left", "Upper", "No transpose", "Non-unit", n, nrhs, &c_b12, &
                a[a_offset], lda, &b[b_offset], ldb);
    } else {

/*        Solve A' * X = B. */

/*        Solve U'*X = B, overwriting B with X. */

        strsm_("Left", "Upper", "Transpose", "Non-unit", n, nrhs, &c_b12, &a[
                a_offset], lda, &b[b_offset], ldb);

/*        Solve L'*X = B, overwriting B with X. */

        strsm_("Left", "Lower", "Transpose", "Unit", n, nrhs, &c_b12, &a[
                a_offset], lda, &b[b_offset], ldb);

/*        Apply row interchanges to the solution vectors. */

        slaswp_(nrhs, &b[b_offset], ldb, &c__1, n, &ipiv[1], &c_n1);
    }

    return 0;

/*     End of SGETRS */

} /* sgetrs_ */