dgetrs.c

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/* DGETRS.F -- translated by f2c (version 19941215).
   You must link the resulting object file with the libraries:
        -lf2c -lm   (in that order)
*/

#include "f2c.h"

/* Table of constant values */

static integer c__1 = 1;
static doublereal c_b12 = 1.;
static integer c_n1 = -1;

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

    /* Local variables */
    extern logical lsame_();
    extern /* Subroutine */ int dtrsm_(), xerbla_(), dlaswp_();
    static logical notran;


/*  -- LAPACK routine (version 1.1) -- */
/*     Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd., */
/*     Courant Institute, Argonne National Lab, and Rice University */
/*     March 31, 1993 */

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

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

/*  DGETRS 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 DGETRF. */

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

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

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

/*  B       (input/output) DOUBLE PRECISION 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 = a_dim1 + 1;
    a -= a_offset;
    --ipiv;
    b_dim1 = *ldb;
    b_offset = b_dim1 + 1;
    b -= b_offset;

    /* Function Body */
    *info = 0;
    notran = lsame_(trans, "N", 1L, 1L);
    if (! notran && ! lsame_(trans, "T", 1L, 1L) && ! lsame_(trans, "C", 1L, 
            1L)) {
        *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_("DGETRS", &i__1, 6L);
        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. */

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

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

        dtrsm_("Left", "Lower", "No transpose", "Unit", n, nrhs, &c_b12, &a[
                a_offset], lda, &b[b_offset], ldb, 4L, 5L, 12L, 4L);

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

        dtrsm_("Left", "Upper", "No transpose", "Non-unit", n, nrhs, &c_b12, &
                a[a_offset], lda, &b[b_offset], ldb, 4L, 5L, 12L, 8L);
    } else {

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

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

        dtrsm_("Left", "Upper", "Transpose", "Non-unit", n, nrhs, &c_b12, &a[
                a_offset], lda, &b[b_offset], ldb, 4L, 5L, 9L, 8L);

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

        dtrsm_("Left", "Lower", "Transpose", "Unit", n, nrhs, &c_b12, &a[
                a_offset], lda, &b[b_offset], ldb, 4L, 5L, 9L, 4L);

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

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

    return 0;

/*     End of DGETRS */

} /* dgetrs_ */

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