strtri.c

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/* strtri.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;
static integer c__2 = 2;
static real c_b18 = 1.f;
static real c_b22 = -1.f;

/* Subroutine */ int strtri_(char *uplo, char *diag, integer *n, real *a, 
        integer *lda, integer *info)
{
    /* System generated locals */
    address a__1[2];
    integer a_dim1, a_offset, i__1, i__2[2], i__3, i__4, i__5;
    char ch__1[2];

    /* Builtin functions */
    /* Subroutine */ int s_cat(char *, char **, integer *, integer *, ftnlen);

    /* Local variables */
    integer j, jb, nb, nn;
    extern logical lsame_(char *, char *);
    logical upper;
    extern /* Subroutine */ int strmm_(char *, char *, char *, char *, 
            integer *, integer *, real *, real *, integer *, real *, integer *
), strsm_(char *, char *, char *, 
            char *, integer *, integer *, real *, real *, integer *, real *, 
            integer *), strti2_(char *, char *
, integer *, real *, integer *, integer *), 
            xerbla_(char *, integer *);
    extern integer ilaenv_(integer *, char *, char *, integer *, integer *, 
            integer *, integer *);
    logical nounit;


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

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

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

/*  STRTRI computes the inverse of a real upper or lower triangular */
/*  matrix A. */

/*  This is the Level 3 BLAS version of the algorithm. */

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

/*  UPLO    (input) CHARACTER*1 */
/*          = 'U':  A is upper triangular; */
/*          = 'L':  A is lower triangular. */

/*  DIAG    (input) CHARACTER*1 */
/*          = 'N':  A is non-unit triangular; */
/*          = 'U':  A is unit triangular. */

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

/*  A       (input/output) REAL array, dimension (LDA,N) */
/*          On entry, the triangular matrix A.  If UPLO = 'U', the */
/*          leading N-by-N upper triangular part of the array A contains */
/*          the upper triangular matrix, and the strictly lower */
/*          triangular part of A is not referenced.  If UPLO = 'L', the */
/*          leading N-by-N lower triangular part of the array A contains */
/*          the lower triangular matrix, and the strictly upper */
/*          triangular part of A is not referenced.  If DIAG = 'U', the */
/*          diagonal elements of A are also not referenced and are */
/*          assumed to be 1. */
/*          On exit, the (triangular) inverse of the original matrix, in */
/*          the same storage format. */

/*  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, A(i,i) is exactly zero.  The triangular */
/*               matrix is singular and its inverse can not be computed. */

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

/*     .. Parameters .. */
/*     .. */
/*     .. Local Scalars .. */
/*     .. */
/*     .. 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;
    upper = lsame_(uplo, "U");
    nounit = lsame_(diag, "N");
    if (! upper && ! lsame_(uplo, "L")) {
        *info = -1;
    } else if (! nounit && ! lsame_(diag, "U")) {
        *info = -2;
    } else if (*n < 0) {
        *info = -3;
    } else if (*lda < max(1,*n)) {
        *info = -5;
    }
    if (*info != 0) {
        i__1 = -(*info);
        xerbla_("STRTRI", &i__1);
        return 0;
    }

/*     Quick return if possible */

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

/*     Check for singularity if non-unit. */

    if (nounit) {
        i__1 = *n;
        for (*info = 1; *info <= i__1; ++(*info)) {
            if (a[*info + *info * a_dim1] == 0.f) {
                return 0;
            }
/* L10: */
        }
        *info = 0;
    }

/*     Determine the block size for this environment. */

/* Writing concatenation */
    i__2[0] = 1, a__1[0] = uplo;
    i__2[1] = 1, a__1[1] = diag;
    s_cat(ch__1, a__1, i__2, &c__2, (ftnlen)2);
    nb = ilaenv_(&c__1, "STRTRI", ch__1, n, &c_n1, &c_n1, &c_n1);
    if (nb <= 1 || nb >= *n) {

/*        Use unblocked code */

        strti2_(uplo, diag, n, &a[a_offset], lda, info);
    } else {

/*        Use blocked code */

        if (upper) {

/*           Compute inverse of upper triangular matrix */

            i__1 = *n;
            i__3 = nb;
            for (j = 1; i__3 < 0 ? j >= i__1 : j <= i__1; j += i__3) {
/* Computing MIN */
                i__4 = nb, i__5 = *n - j + 1;
                jb = min(i__4,i__5);

/*              Compute rows 1:j-1 of current block column */

                i__4 = j - 1;
                strmm_("Left", "Upper", "No transpose", diag, &i__4, &jb, &
                        c_b18, &a[a_offset], lda, &a[j * a_dim1 + 1], lda);
                i__4 = j - 1;
                strsm_("Right", "Upper", "No transpose", diag, &i__4, &jb, &
                        c_b22, &a[j + j * a_dim1], lda, &a[j * a_dim1 + 1], 
                        lda);

/*              Compute inverse of current diagonal block */

                strti2_("Upper", diag, &jb, &a[j + j * a_dim1], lda, info);
/* L20: */
            }
        } else {

/*           Compute inverse of lower triangular matrix */

            nn = (*n - 1) / nb * nb + 1;
            i__3 = -nb;
            for (j = nn; i__3 < 0 ? j >= 1 : j <= 1; j += i__3) {
/* Computing MIN */
                i__1 = nb, i__4 = *n - j + 1;
                jb = min(i__1,i__4);
                if (j + jb <= *n) {

/*                 Compute rows j+jb:n of current block column */

                    i__1 = *n - j - jb + 1;
                    strmm_("Left", "Lower", "No transpose", diag, &i__1, &jb, 
                            &c_b18, &a[j + jb + (j + jb) * a_dim1], lda, &a[j 
                            + jb + j * a_dim1], lda);
                    i__1 = *n - j - jb + 1;
                    strsm_("Right", "Lower", "No transpose", diag, &i__1, &jb, 
                             &c_b22, &a[j + j * a_dim1], lda, &a[j + jb + j * 
                            a_dim1], lda);
                }

/*              Compute inverse of current diagonal block */

                strti2_("Lower", diag, &jb, &a[j + j * a_dim1], lda, info);
/* L30: */
            }
        }
    }

    return 0;

/*     End of STRTRI */

} /* strtri_ */