dgttrs.c

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/* dgttrs.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 integer c_n1 = -1;

/* Subroutine */ int dgttrs_(char *trans, integer *n, integer *nrhs, 
        doublereal *dl, doublereal *d__, doublereal *du, doublereal *du2, 
        integer *ipiv, doublereal *b, integer *ldb, integer *info)
{
    /* System generated locals */
    integer b_dim1, b_offset, i__1, i__2, i__3;

    /* Local variables */
    integer j, jb, nb;
    extern /* Subroutine */ int dgtts2_(integer *, integer *, integer *, 
            doublereal *, doublereal *, doublereal *, doublereal *, integer *, 
             doublereal *, integer *), xerbla_(char *, integer *);
    extern integer ilaenv_(integer *, char *, char *, integer *, integer *, 
            integer *, integer *);
    integer itrans;
    logical notran;


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

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

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

/*  DGTTRS solves one of the systems of equations */
/*     A*X = B  or  A'*X = B, */
/*  with a tridiagonal matrix A using the LU factorization computed */
/*  by DGTTRF. */

/*  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. */

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

/*  DL      (input) DOUBLE PRECISION array, dimension (N-1) */
/*          The (n-1) multipliers that define the matrix L from the */
/*          LU factorization of A. */

/*  D       (input) DOUBLE PRECISION array, dimension (N) */
/*          The n diagonal elements of the upper triangular matrix U from */
/*          the LU factorization of A. */

/*  DU      (input) DOUBLE PRECISION array, dimension (N-1) */
/*          The (n-1) elements of the first super-diagonal of U. */

/*  DU2     (input) DOUBLE PRECISION array, dimension (N-2) */
/*          The (n-2) elements of the second super-diagonal of U. */

/*  IPIV    (input) INTEGER array, dimension (N) */
/*          The pivot indices; for 1 <= i <= n, row i of the matrix was */
/*          interchanged with row IPIV(i).  IPIV(i) will always be either */
/*          i or i+1; IPIV(i) = i indicates a row interchange was not */
/*          required. */

/*  B       (input/output) DOUBLE PRECISION array, dimension (LDB,NRHS) */
/*          On entry, the matrix of right hand side vectors B. */
/*          On exit, B is overwritten by the solution vectors 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 */

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

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

    /* Parameter adjustments */
    --dl;
    --d__;
    --du;
    --du2;
    --ipiv;
    b_dim1 = *ldb;
    b_offset = 1 + b_dim1;
    b -= b_offset;

    /* Function Body */
    *info = 0;
    notran = *(unsigned char *)trans == 'N' || *(unsigned char *)trans == 'n';
    if (! notran && ! (*(unsigned char *)trans == 'T' || *(unsigned char *)
            trans == 't') && ! (*(unsigned char *)trans == 'C' || *(unsigned 
            char *)trans == 'c')) {
        *info = -1;
    } else if (*n < 0) {
        *info = -2;
    } else if (*nrhs < 0) {
        *info = -3;
    } else if (*ldb < max(*n,1)) {
        *info = -10;
    }
    if (*info != 0) {
        i__1 = -(*info);
        xerbla_("DGTTRS", &i__1);
        return 0;
    }

/*     Quick return if possible */

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

/*     Decode TRANS */

    if (notran) {
        itrans = 0;
    } else {
        itrans = 1;
    }

/*     Determine the number of right-hand sides to solve at a time. */

    if (*nrhs == 1) {
        nb = 1;
    } else {
/* Computing MAX */
        i__1 = 1, i__2 = ilaenv_(&c__1, "DGTTRS", trans, n, nrhs, &c_n1, &
                c_n1);
        nb = max(i__1,i__2);
    }

    if (nb >= *nrhs) {
        dgtts2_(&itrans, n, nrhs, &dl[1], &d__[1], &du[1], &du2[1], &ipiv[1], 
                &b[b_offset], ldb);
    } else {
        i__1 = *nrhs;
        i__2 = nb;
        for (j = 1; i__2 < 0 ? j >= i__1 : j <= i__1; j += i__2) {
/* Computing MIN */
            i__3 = *nrhs - j + 1;
            jb = min(i__3,nb);
            dgtts2_(&itrans, n, &jb, &dl[1], &d__[1], &du[1], &du2[1], &ipiv[
                    1], &b[j * b_dim1 + 1], ldb);
/* L10: */
        }
    }

/*     End of DGTTRS */

    return 0;
} /* dgttrs_ */