sspsv.c

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/* sspsv.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 sspsv_(char *uplo, integer *n, integer *nrhs, real *ap, 
        integer *ipiv, real *b, integer *ldb, integer *info)
{
    /* System generated locals */
    integer b_dim1, b_offset, i__1;

    /* Local variables */
    extern logical lsame_(char *, char *);
    extern /* Subroutine */ int xerbla_(char *, integer *), ssptrf_(
            char *, integer *, real *, integer *, integer *), ssptrs_(
            char *, integer *, integer *, real *, integer *, real *, integer *
, integer *);


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

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

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

/*  SSPSV computes the solution to a real system of linear equations */
/*     A * X = B, */
/*  where A is an N-by-N symmetric matrix stored in packed format and X */
/*  and B are N-by-NRHS matrices. */

/*  The diagonal pivoting method is used to factor A as */
/*     A = U * D * U**T,  if UPLO = 'U', or */
/*     A = L * D * L**T,  if UPLO = 'L', */
/*  where U (or L) is a product of permutation and unit upper (lower) */
/*  triangular matrices, D is symmetric and block diagonal with 1-by-1 */
/*  and 2-by-2 diagonal blocks.  The factored form of A is then used to */
/*  solve the system of equations A * X = B. */

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

/*  UPLO    (input) CHARACTER*1 */
/*          = 'U':  Upper triangle of A is stored; */
/*          = 'L':  Lower triangle of A is stored. */

/*  N       (input) INTEGER */
/*          The number of linear equations, i.e., 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. */

/*  AP      (input/output) REAL array, dimension (N*(N+1)/2) */
/*          On entry, the upper or lower triangle of the symmetric matrix */
/*          A, packed columnwise in a linear array.  The j-th column of A */
/*          is stored in the array AP as follows: */
/*          if UPLO = 'U', AP(i + (j-1)*j/2) = A(i,j) for 1<=i<=j; */
/*          if UPLO = 'L', AP(i + (j-1)*(2n-j)/2) = A(i,j) for j<=i<=n. */
/*          See below for further details. */

/*          On exit, the block diagonal matrix D and the multipliers used */
/*          to obtain the factor U or L from the factorization */
/*          A = U*D*U**T or A = L*D*L**T as computed by SSPTRF, stored as */
/*          a packed triangular matrix in the same storage format as A. */

/*  IPIV    (output) INTEGER array, dimension (N) */
/*          Details of the interchanges and the block structure of D, as */
/*          determined by SSPTRF.  If IPIV(k) > 0, then rows and columns */
/*          k and IPIV(k) were interchanged, and D(k,k) is a 1-by-1 */
/*          diagonal block.  If UPLO = 'U' and IPIV(k) = IPIV(k-1) < 0, */
/*          then rows and columns k-1 and -IPIV(k) were interchanged and */
/*          D(k-1:k,k-1:k) is a 2-by-2 diagonal block.  If UPLO = 'L' and */
/*          IPIV(k) = IPIV(k+1) < 0, then rows and columns k+1 and */
/*          -IPIV(k) were interchanged and D(k:k+1,k:k+1) is a 2-by-2 */
/*          diagonal block. */

/*  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, D(i,i) is exactly zero.  The factorization */
/*                has been completed, but the block diagonal matrix D is */
/*                exactly singular, so the solution could not be */
/*                computed. */

/*  Further Details */
/*  =============== */

/*  The packed storage scheme is illustrated by the following example */
/*  when N = 4, UPLO = 'U': */

/*  Two-dimensional storage of the symmetric matrix A: */

/*     a11 a12 a13 a14 */
/*         a22 a23 a24 */
/*             a33 a34     (aij = aji) */
/*                 a44 */

/*  Packed storage of the upper triangle of A: */

/*  AP = [ a11, a12, a22, a13, a23, a33, a14, a24, a34, a44 ] */

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

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

/*     Test the input parameters. */

    /* Parameter adjustments */
    --ap;
    --ipiv;
    b_dim1 = *ldb;
    b_offset = 1 + b_dim1;
    b -= b_offset;

    /* Function Body */
    *info = 0;
    if (! lsame_(uplo, "U") && ! lsame_(uplo, "L")) {
        *info = -1;
    } else if (*n < 0) {
        *info = -2;
    } else if (*nrhs < 0) {
        *info = -3;
    } else if (*ldb < max(1,*n)) {
        *info = -7;
    }
    if (*info != 0) {
        i__1 = -(*info);
        xerbla_("SSPSV ", &i__1);
        return 0;
    }

/*     Compute the factorization A = U*D*U' or A = L*D*L'. */

    ssptrf_(uplo, n, &ap[1], &ipiv[1], info);
    if (*info == 0) {

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

        ssptrs_(uplo, n, nrhs, &ap[1], &ipiv[1], &b[b_offset], ldb, info);

    }
    return 0;

/*     End of SSPSV */

} /* sspsv_ */