spotri.c

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/* spotri.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 spotri_(char *uplo, integer *n, real *a, integer *lda, 
        integer *info)
{
    /* System generated locals */
    integer a_dim1, a_offset, i__1;

    /* Local variables */
    extern logical lsame_(char *, char *);
    extern /* Subroutine */ int xerbla_(char *, integer *), slauum_(
            char *, integer *, real *, integer *, integer *), strtri_(
            char *, char *, integer *, 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 */
/*  ======= */

/*  SPOTRI computes the inverse of a real symmetric positive definite */
/*  matrix A using the Cholesky factorization A = U**T*U or A = L*L**T */
/*  computed by SPOTRF. */

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

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

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

/*  A       (input/output) REAL array, dimension (LDA,N) */
/*          On entry, the triangular factor U or L from the Cholesky */
/*          factorization A = U**T*U or A = L*L**T, as computed by */
/*          SPOTRF. */
/*          On exit, the upper or lower triangle of the (symmetric) */
/*          inverse of A, overwriting the input factor U or L. */

/*  LDA     (input) INTEGER */
/*          The leading dimension of the array A.  LDA >= 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 (i,i) element of the factor U or L is */
/*                zero, and the inverse could not be computed. */

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

/*     .. 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;

    /* Function Body */
    *info = 0;
    if (! lsame_(uplo, "U") && ! lsame_(uplo, "L")) {
        *info = -1;
    } else if (*n < 0) {
        *info = -2;
    } else if (*lda < max(1,*n)) {
        *info = -4;
    }
    if (*info != 0) {
        i__1 = -(*info);
        xerbla_("SPOTRI", &i__1);
        return 0;
    }

/*     Quick return if possible */

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

/*     Invert the triangular Cholesky factor U or L. */

    strtri_(uplo, "Non-unit", n, &a[a_offset], lda, info);
    if (*info > 0) {
        return 0;
    }

/*     Form inv(U)*inv(U)' or inv(L)'*inv(L). */

    slauum_(uplo, n, &a[a_offset], lda, info);

    return 0;

/*     End of SPOTRI */

} /* spotri_ */