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/* lapack/single/sgeqr2.f -- translated by f2c (version 20050501).
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
*/
#ifdef __cplusplus
extern "C" {
#endif
#include "v3p_netlib.h"
/* Table of constant values */
static integer c__1 = 1;
/*< SUBROUTINE SGEQR2( M, N, A, LDA, TAU, WORK, INFO ) >*/
/* Subroutine */ int sgeqr2_(integer *m, integer *n, real *a, integer *lda,
real *tau, real *work, integer *info)
{
/* System generated locals */
integer a_dim1, a_offset, i__1, i__2, i__3;
/* Local variables */
integer i__, k;
real aii;
extern /* Subroutine */ int slarf_(char *, integer *, integer *, real *,
integer *, real *, real *, integer *, real *, ftnlen), xerbla_(
char *, integer *, ftnlen), slarfg_(integer *, real *, real *,
integer *, real *);
/* -- LAPACK routine (version 3.0) -- */
/* Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd., */
/* Courant Institute, Argonne National Lab, and Rice University */
/* February 29, 1992 */
/* .. Scalar Arguments .. */
/*< INTEGER INFO, LDA, M, N >*/
/* .. */
/* .. Array Arguments .. */
/*< REAL A( LDA, * ), TAU( * ), WORK( * ) >*/
/* .. */
/* Purpose */
/* ======= */
/* SGEQR2 computes a QR factorization of a real m by n matrix A: */
/* A = Q * R. */
/* Arguments */
/* ========= */
/* M (input) INTEGER */
/* The number of rows of the matrix A. M >= 0. */
/* N (input) INTEGER */
/* The number of columns of the matrix A. N >= 0. */
/* A (input/output) REAL array, dimension (LDA,N) */
/* On entry, the m by n matrix A. */
/* On exit, the elements on and above the diagonal of the array */
/* contain the min(m,n) by n upper trapezoidal matrix R (R is */
/* upper triangular if m >= n); the elements below the diagonal, */
/* with the array TAU, represent the orthogonal matrix Q as a */
/* product of elementary reflectors (see Further Details). */
/* LDA (input) INTEGER */
/* The leading dimension of the array A. LDA >= max(1,M). */
/* TAU (output) REAL array, dimension (min(M,N)) */
/* The scalar factors of the elementary reflectors (see Further */
/* Details). */
/* WORK (workspace) REAL array, dimension (N) */
/* INFO (output) INTEGER */
/* = 0: successful exit */
/* < 0: if INFO = -i, the i-th argument had an illegal value */
/* Further Details */
/* =============== */
/* The matrix Q is represented as a product of elementary reflectors */
/* Q = H(1) H(2) . . . H(k), where k = min(m,n). */
/* Each H(i) has the form */
/* H(i) = I - tau * v * v' */
/* where tau is a real scalar, and v is a real vector with */
/* v(1:i-1) = 0 and v(i) = 1; v(i+1:m) is stored on exit in A(i+1:m,i), */
/* and tau in TAU(i). */
/* ===================================================================== */
/* .. Parameters .. */
/*< REAL ONE >*/
/*< PARAMETER ( ONE = 1.0E+0 ) >*/
/* .. */
/* .. Local Scalars .. */
/*< INTEGER I, K >*/
/*< REAL AII >*/
/* .. */
/* .. External Subroutines .. */
/*< EXTERNAL SLARF, SLARFG, XERBLA >*/
/* .. */
/* .. Intrinsic Functions .. */
/*< INTRINSIC MAX, MIN >*/
/* .. */
/* .. Executable Statements .. */
/* Test the input arguments */
/*< INFO = 0 >*/
/* Parameter adjustments */
a_dim1 = *lda;
a_offset = 1 + a_dim1;
a -= a_offset;
--tau;
--work;
/* Function Body */
*info = 0;
/*< IF( M.LT.0 ) THEN >*/
if (*m < 0) {
/*< INFO = -1 >*/
*info = -1;
/*< ELSE IF( N.LT.0 ) THEN >*/
} else if (*n < 0) {
/*< INFO = -2 >*/
*info = -2;
/*< ELSE IF( LDA.LT.MAX( 1, M ) ) THEN >*/
} else if (*lda < max(1,*m)) {
/*< INFO = -4 >*/
*info = -4;
/*< END IF >*/
}
/*< IF( INFO.NE.0 ) THEN >*/
if (*info != 0) {
/*< CALL XERBLA( 'SGEQR2', -INFO ) >*/
i__1 = -(*info);
xerbla_("SGEQR2", &i__1, (ftnlen)6);
/*< RETURN >*/
return 0;
/*< END IF >*/
}
/*< K = MIN( M, N ) >*/
k = min(*m,*n);
/*< DO 10 I = 1, K >*/
i__1 = k;
for (i__ = 1; i__ <= i__1; ++i__) {
/* Generate elementary reflector H(i) to annihilate A(i+1:m,i) */
/*< >*/
i__2 = *m - i__ + 1;
/* Computing MIN */
i__3 = i__ + 1;
slarfg_(&i__2, &a[i__ + i__ * a_dim1], &a[min(i__3,*m) + i__ * a_dim1]
, &c__1, &tau[i__]);
/*< IF( I.LT.N ) THEN >*/
if (i__ < *n) {
/* Apply H(i) to A(i:m,i+1:n) from the left */
/*< AII = A( I, I ) >*/
aii = a[i__ + i__ * a_dim1];
/*< A( I, I ) = ONE >*/
a[i__ + i__ * a_dim1] = (float)1.;
/*< >*/
i__2 = *m - i__ + 1;
i__3 = *n - i__;
slarf_("Left", &i__2, &i__3, &a[i__ + i__ * a_dim1], &c__1, &tau[
i__], &a[i__ + (i__ + 1) * a_dim1], lda, &work[1], (
ftnlen)4);
/*< A( I, I ) = AII >*/
a[i__ + i__ * a_dim1] = aii;
/*< END IF >*/
}
/*< 10 CONTINUE >*/
/* L10: */
}
/*< RETURN >*/
return 0;
/* End of SGEQR2 */
/*< END >*/
} /* sgeqr2_ */
#ifdef __cplusplus
}
#endif
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