sptsv.c

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/* sptsv.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"

/* Subroutine */ int sptsv_(integer *n, integer *nrhs, real *d__, real *e, 
        real *b, integer *ldb, integer *info)
{
    /* System generated locals */
    integer b_dim1, b_offset, i__1;

    /* Local variables */
    extern /* Subroutine */ int xerbla_(char *, integer *), spttrf_(
            integer *, real *, real *, integer *), spttrs_(integer *, integer 
            *, real *, real *, real *, integer *, integer *);


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

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

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

/*  SPTSV computes the solution to a real system of linear equations */
/*  A*X = B, where A is an N-by-N symmetric positive definite tridiagonal */
/*  matrix, and X and B are N-by-NRHS matrices. */

/*  A is factored as A = L*D*L**T, and the factored form of A is then */
/*  used to solve the system of equations. */

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

/*  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. */

/*  D       (input/output) REAL array, dimension (N) */
/*          On entry, the n diagonal elements of the tridiagonal matrix */
/*          A.  On exit, the n diagonal elements of the diagonal matrix */
/*          D from the factorization A = L*D*L**T. */

/*  E       (input/output) REAL array, dimension (N-1) */
/*          On entry, the (n-1) subdiagonal elements of the tridiagonal */
/*          matrix A.  On exit, the (n-1) subdiagonal elements of the */
/*          unit bidiagonal factor L from the L*D*L**T factorization of */
/*          A.  (E can also be regarded as the superdiagonal of the unit */
/*          bidiagonal factor U from the U**T*D*U factorization of A.) */

/*  B       (input/output) REAL array, dimension (LDB,NRHS) */
/*          On entry, the N-by-NRHS right hand side matrix B. */
/*          On exit, if INFO = 0, the N-by-NRHS 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 */
/*          > 0:  if INFO = i, the leading minor of order i is not */
/*                positive definite, and the solution has not been */
/*                computed.  The factorization has not been completed */
/*                unless i = N. */

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

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

/*     Test the input parameters. */

    /* Parameter adjustments */
    --d__;
    --e;
    b_dim1 = *ldb;
    b_offset = 1 + b_dim1;
    b -= b_offset;

    /* Function Body */
    *info = 0;
    if (*n < 0) {
        *info = -1;
    } else if (*nrhs < 0) {
        *info = -2;
    } else if (*ldb < max(1,*n)) {
        *info = -6;
    }
    if (*info != 0) {
        i__1 = -(*info);
        xerbla_("SPTSV ", &i__1);
        return 0;
    }

/*     Compute the L*D*L' (or U'*D*U) factorization of A. */

    spttrf_(n, &d__[1], &e[1], info);
    if (*info == 0) {

/*        Solve the system A*X = B, overwriting B with X. */

        spttrs_(n, nrhs, &d__[1], &e[1], &b[b_offset], ldb, info);
    }
    return 0;

/*     End of SPTSV */

} /* sptsv_ */