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171 lines
4.5 KiB
C
171 lines
4.5 KiB
C
#include "clapack.h"
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/* Table of constant values */
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static integer c__1 = 1;
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/* Subroutine */ int strti2_(char *uplo, char *diag, integer *n, real *a,
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integer *lda, integer *info)
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{
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/* System generated locals */
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integer a_dim1, a_offset, i__1, i__2;
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/* Local variables */
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integer j;
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real ajj;
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extern logical lsame_(char *, char *);
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extern /* Subroutine */ int sscal_(integer *, real *, real *, integer *);
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logical upper;
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extern /* Subroutine */ int strmv_(char *, char *, char *, integer *,
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real *, integer *, real *, integer *),
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xerbla_(char *, integer *);
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logical nounit;
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/* -- LAPACK routine (version 3.1) -- */
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/* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. */
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/* November 2006 */
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/* .. Scalar Arguments .. */
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/* .. */
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/* .. Array Arguments .. */
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/* .. */
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/* Purpose */
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/* ======= */
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/* STRTI2 computes the inverse of a real upper or lower triangular */
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/* matrix. */
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/* This is the Level 2 BLAS version of the algorithm. */
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/* Arguments */
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/* ========= */
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/* UPLO (input) CHARACTER*1 */
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/* Specifies whether the matrix A is upper or lower triangular. */
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/* = 'U': Upper triangular */
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/* = 'L': Lower triangular */
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/* DIAG (input) CHARACTER*1 */
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/* Specifies whether or not the matrix A is unit triangular. */
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/* = 'N': Non-unit triangular */
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/* = 'U': Unit triangular */
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/* N (input) INTEGER */
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/* The order of the matrix A. N >= 0. */
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/* A (input/output) REAL array, dimension (LDA,N) */
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/* On entry, the triangular matrix A. If UPLO = 'U', the */
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/* leading n by n upper triangular part of the array A contains */
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/* the upper triangular matrix, and the strictly lower */
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/* triangular part of A is not referenced. If UPLO = 'L', the */
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/* leading n by n lower triangular part of the array A contains */
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/* the lower triangular matrix, and the strictly upper */
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/* triangular part of A is not referenced. If DIAG = 'U', the */
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/* diagonal elements of A are also not referenced and are */
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/* assumed to be 1. */
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/* On exit, the (triangular) inverse of the original matrix, in */
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/* the same storage format. */
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/* LDA (input) INTEGER */
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/* The leading dimension of the array A. LDA >= max(1,N). */
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/* INFO (output) INTEGER */
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/* = 0: successful exit */
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/* < 0: if INFO = -k, the k-th argument had an illegal value */
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/* ===================================================================== */
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/* .. Parameters .. */
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/* .. */
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/* .. Local Scalars .. */
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/* .. */
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/* .. External Functions .. */
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/* .. */
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/* .. External Subroutines .. */
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/* .. */
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/* .. Intrinsic Functions .. */
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/* .. */
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/* .. Executable Statements .. */
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/* Test the input parameters. */
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/* Parameter adjustments */
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a_dim1 = *lda;
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a_offset = 1 + a_dim1;
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a -= a_offset;
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/* Function Body */
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*info = 0;
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upper = lsame_(uplo, "U");
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nounit = lsame_(diag, "N");
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if (! upper && ! lsame_(uplo, "L")) {
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*info = -1;
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} else if (! nounit && ! lsame_(diag, "U")) {
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*info = -2;
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} else if (*n < 0) {
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*info = -3;
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} else if (*lda < max(1,*n)) {
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*info = -5;
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}
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if (*info != 0) {
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i__1 = -(*info);
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xerbla_("STRTI2", &i__1);
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return 0;
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}
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if (upper) {
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/* Compute inverse of upper triangular matrix. */
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i__1 = *n;
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for (j = 1; j <= i__1; ++j) {
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if (nounit) {
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a[j + j * a_dim1] = 1.f / a[j + j * a_dim1];
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ajj = -a[j + j * a_dim1];
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} else {
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ajj = -1.f;
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}
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/* Compute elements 1:j-1 of j-th column. */
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i__2 = j - 1;
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strmv_("Upper", "No transpose", diag, &i__2, &a[a_offset], lda, &
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a[j * a_dim1 + 1], &c__1);
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i__2 = j - 1;
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sscal_(&i__2, &ajj, &a[j * a_dim1 + 1], &c__1);
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/* L10: */
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}
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} else {
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/* Compute inverse of lower triangular matrix. */
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for (j = *n; j >= 1; --j) {
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if (nounit) {
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a[j + j * a_dim1] = 1.f / a[j + j * a_dim1];
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ajj = -a[j + j * a_dim1];
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} else {
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ajj = -1.f;
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}
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if (j < *n) {
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/* Compute elements j+1:n of j-th column. */
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i__1 = *n - j;
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strmv_("Lower", "No transpose", diag, &i__1, &a[j + 1 + (j +
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1) * a_dim1], lda, &a[j + 1 + j * a_dim1], &c__1);
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i__1 = *n - j;
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sscal_(&i__1, &ajj, &a[j + 1 + j * a_dim1], &c__1);
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}
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/* L20: */
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}
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}
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return 0;
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/* End of STRTI2 */
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} /* strti2_ */
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