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180 lines
4.6 KiB
C
180 lines
4.6 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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static real c_b8 = -1.f;
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/* Subroutine */ int sgetf2_(integer *m, integer *n, real *a, integer *lda,
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integer *ipiv, 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, i__3;
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real r__1;
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/* Local variables */
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integer i__, j, jp;
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extern /* Subroutine */ int sger_(integer *, integer *, real *, real *,
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integer *, real *, integer *, real *, integer *), sscal_(integer *
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, real *, real *, integer *);
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real sfmin;
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extern /* Subroutine */ int sswap_(integer *, real *, integer *, real *,
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integer *);
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extern doublereal slamch_(char *);
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extern /* Subroutine */ int xerbla_(char *, integer *);
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extern integer isamax_(integer *, real *, integer *);
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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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/* SGETF2 computes an LU factorization of a general m-by-n matrix A */
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/* using partial pivoting with row interchanges. */
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/* The factorization has the form */
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/* A = P * L * U */
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/* where P is a permutation matrix, L is lower triangular with unit */
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/* diagonal elements (lower trapezoidal if m > n), and U is upper */
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/* triangular (upper trapezoidal if m < n). */
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/* This is the right-looking Level 2 BLAS version of the algorithm. */
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/* Arguments */
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/* ========= */
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/* M (input) INTEGER */
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/* The number of rows of the matrix A. M >= 0. */
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/* N (input) INTEGER */
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/* The number of columns 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 m by n matrix to be factored. */
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/* On exit, the factors L and U from the factorization */
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/* A = P*L*U; the unit diagonal elements of L are not stored. */
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/* LDA (input) INTEGER */
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/* The leading dimension of the array A. LDA >= max(1,M). */
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/* IPIV (output) INTEGER array, dimension (min(M,N)) */
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/* The pivot indices; for 1 <= i <= min(M,N), row i of the */
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/* matrix was interchanged with row IPIV(i). */
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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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/* > 0: if INFO = k, U(k,k) is exactly zero. The factorization */
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/* has been completed, but the factor U is exactly */
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/* singular, and division by zero will occur if it is used */
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/* to solve a system of equations. */
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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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--ipiv;
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/* Function Body */
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*info = 0;
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if (*m < 0) {
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*info = -1;
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} else if (*n < 0) {
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*info = -2;
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} else if (*lda < max(1,*m)) {
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*info = -4;
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}
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if (*info != 0) {
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i__1 = -(*info);
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xerbla_("SGETF2", &i__1);
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return 0;
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}
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/* Quick return if possible */
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if (*m == 0 || *n == 0) {
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return 0;
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}
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/* Compute machine safe minimum */
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sfmin = slamch_("S");
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i__1 = min(*m,*n);
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for (j = 1; j <= i__1; ++j) {
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/* Find pivot and test for singularity. */
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i__2 = *m - j + 1;
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jp = j - 1 + isamax_(&i__2, &a[j + j * a_dim1], &c__1);
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ipiv[j] = jp;
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if (a[jp + j * a_dim1] != 0.f) {
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/* Apply the interchange to columns 1:N. */
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if (jp != j) {
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sswap_(n, &a[j + a_dim1], lda, &a[jp + a_dim1], lda);
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}
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/* Compute elements J+1:M of J-th column. */
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if (j < *m) {
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if ((r__1 = a[j + j * a_dim1], dabs(r__1)) >= sfmin) {
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i__2 = *m - j;
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r__1 = 1.f / a[j + j * a_dim1];
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sscal_(&i__2, &r__1, &a[j + 1 + j * a_dim1], &c__1);
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} else {
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i__2 = *m - j;
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for (i__ = 1; i__ <= i__2; ++i__) {
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a[j + i__ + j * a_dim1] /= a[j + j * a_dim1];
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/* L20: */
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}
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}
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}
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} else if (*info == 0) {
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*info = j;
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}
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if (j < min(*m,*n)) {
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/* Update trailing submatrix. */
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i__2 = *m - j;
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i__3 = *n - j;
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sger_(&i__2, &i__3, &c_b8, &a[j + 1 + j * a_dim1], &c__1, &a[j + (
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j + 1) * a_dim1], lda, &a[j + 1 + (j + 1) * a_dim1], lda);
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}
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/* L10: */
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}
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return 0;
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/* End of SGETF2 */
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} /* sgetf2_ */
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