/* clapll.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 clapll_(integer *n, complex *x, integer *incx, complex *
y, integer *incy, real *ssmin)
{
/* System generated locals */
integer i__1;
real r__1, r__2, r__3;
complex q__1, q__2, q__3, q__4;
/* Builtin functions */
void r_cnjg(complex *, complex *);
double c_abs(complex *);
/* Local variables */
complex c__, a11, a12, a22, tau;
extern /* Subroutine */ int slas2_(real *, real *, real *, real *, real *)
;
extern /* Complex */ VOID cdotc_(complex *, integer *, complex *, integer
*, complex *, integer *);
extern /* Subroutine */ int caxpy_(integer *, complex *, complex *,
integer *, complex *, integer *);
real ssmax;
extern /* Subroutine */ int clarfg_(integer *, complex *, complex *,
integer *, complex *);
/* -- LAPACK auxiliary routine (version 3.2) -- */
/* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. */
/* November 2006 */
/* .. Scalar Arguments .. */
/* .. */
/* .. Array Arguments .. */
/* .. */
/* Purpose */
/* ======= */
/* Given two column vectors X and Y, let */
/* A = ( X Y ). */
/* The subroutine first computes the QR factorization of A = Q*R, */
/* and then computes the SVD of the 2-by-2 upper triangular matrix R. */
/* The smaller singular value of R is returned in SSMIN, which is used */
/* as the measurement of the linear dependency of the vectors X and Y. */
/* Arguments */
/* ========= */
/* N (input) INTEGER */
/* The length of the vectors X and Y. */
/* X (input/output) COMPLEX array, dimension (1+(N-1)*INCX) */
/* On entry, X contains the N-vector X. */
/* On exit, X is overwritten. */
/* INCX (input) INTEGER */
/* The increment between successive elements of X. INCX > 0. */
/* Y (input/output) COMPLEX array, dimension (1+(N-1)*INCY) */
/* On entry, Y contains the N-vector Y. */
/* On exit, Y is overwritten. */
/* INCY (input) INTEGER */
/* The increment between successive elements of Y. INCY > 0. */
/* SSMIN (output) REAL */
/* The smallest singular value of the N-by-2 matrix A = ( X Y ). */
/* ===================================================================== */
/* .. Parameters .. */
/* .. */
/* .. Local Scalars .. */
/* .. */
/* .. Intrinsic Functions .. */
/* .. */
/* .. External Functions .. */
/* .. */
/* .. External Subroutines .. */
/* .. */
/* .. Executable Statements .. */
/* Quick return if possible */
/* Parameter adjustments */
--y;
--x;
/* Function Body */
if (*n <= 1) {
*ssmin = 0.f;
return 0;
}
/* Compute the QR factorization of the N-by-2 matrix ( X Y ) */
clarfg_(n, &x[1], &x[*incx + 1], incx, &tau);
a11.r = x[1].r, a11.i = x[1].i;
x[1].r = 1.f, x[1].i = 0.f;
r_cnjg(&q__3, &tau);
q__2.r = -q__3.r, q__2.i = -q__3.i;
cdotc_(&q__4, n, &x[1], incx, &y[1], incy);
q__1.r = q__2.r * q__4.r - q__2.i * q__4.i, q__1.i = q__2.r * q__4.i +
q__2.i * q__4.r;
c__.r = q__1.r, c__.i = q__1.i;
caxpy_(n, &c__, &x[1], incx, &y[1], incy);
i__1 = *n - 1;
clarfg_(&i__1, &y[*incy + 1], &y[(*incy << 1) + 1], incy, &tau);
a12.r = y[1].r, a12.i = y[1].i;
i__1 = *incy + 1;
a22.r = y[i__1].r, a22.i = y[i__1].i;
/* Compute the SVD of 2-by-2 Upper triangular matrix. */
r__1 = c_abs(&a11);
r__2 = c_abs(&a12);
r__3 = c_abs(&a22);
slas2_(&r__1, &r__2, &r__3, ssmin, &ssmax);
return 0;
/* End of CLAPLL */
} /* clapll_ */
