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/* ../../../dependencies/lapack/src/slasq1.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"
/* Table of constant values */
static integer c__1 = 1;
static integer c__2 = 2;
static integer c__0 = 0;
/* Subroutine */ int slasq1_(integer *n, real *d__, real *e, real *work,
integer *info)
{
/* System generated locals */
integer i__1, i__2;
real r__1, r__2, r__3;
/* Builtin functions */
double sqrt(doublereal);
/* Local variables */
static integer i__;
static real eps;
extern /* Subroutine */ int slas2_(real *, real *, real *, real *, real *)
;
static real scale;
static integer iinfo;
static real sigmn, sigmx;
extern /* Subroutine */ int scopy_(integer *, real *, integer *, real *,
integer *), slasq2_(integer *, real *, integer *);
extern doublereal slamch_(char *, ftnlen);
static real safmin;
extern /* Subroutine */ int xerbla_(char *, integer *, ftnlen), slascl_(
char *, integer *, integer *, real *, real *, integer *, integer *
, real *, integer *, integer *, ftnlen), slasrt_(char *, integer *
, real *, integer *, ftnlen);
/* -- LAPACK routine (version 3.0) -- */
/* Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd., */
/* Courant Institute, Argonne National Lab, and Rice University */
/* October 31, 1999 */
/* .. Scalar Arguments .. */
/* .. */
/* .. Array Arguments .. */
/* .. */
/* Purpose */
/* ======= */
/* SLASQ1 computes the singular values of a real N-by-N bidiagonal */
/* matrix with diagonal D and off-diagonal E. The singular values */
/* are computed to high relative accuracy, in the absence of */
/* denormalization, underflow and overflow. The algorithm was first */
/* presented in */
/* "Accurate singular values and differential qd algorithms" by K. V. */
/* Fernando and B. N. Parlett, Numer. Math., Vol-67, No. 2, pp. 191-230, */
/* 1994, */
/* and the present implementation is described in "An implementation of */
/* the dqds Algorithm (Positive Case)", LAPACK Working Note. */
/* Arguments */
/* ========= */
/* N (input) INTEGER */
/* The number of rows and columns in the matrix. N >= 0. */
/* D (input/output) REAL array, dimension (N) */
/* On entry, D contains the diagonal elements of the */
/* bidiagonal matrix whose SVD is desired. On normal exit, */
/* D contains the singular values in decreasing order. */
/* E (input/output) REAL array, dimension (N) */
/* On entry, elements E(1:N-1) contain the off-diagonal elements */
/* of the bidiagonal matrix whose SVD is desired. */
/* On exit, E is overwritten. */
/* WORK (workspace) REAL array, dimension (4*N) */
/* INFO (output) INTEGER */
/* = 0: successful exit */
/* < 0: if INFO = -i, the i-th argument had an illegal value */
/* > 0: the algorithm failed */
/* = 1, a split was marked by a positive value in E */
/* = 2, current block of Z not diagonalized after 30*N */
/* iterations (in inner while loop) */
/* = 3, termination criterion of outer while loop not met */
/* (program created more than N unreduced blocks) */
/* ===================================================================== */
/* .. Parameters .. */
/* .. */
/* .. Local Scalars .. */
/* .. */
/* .. External Subroutines .. */
/* .. */
/* .. External Functions .. */
/* .. */
/* .. Intrinsic Functions .. */
/* .. */
/* .. Executable Statements .. */
/* Parameter adjustments */
--work;
--e;
--d__;
/* Function Body */
*info = 0;
if (*n < 0) {
*info = -2;
i__1 = -(*info);
xerbla_("SLASQ1", &i__1, (ftnlen)6);
return 0;
} else if (*n == 0) {
return 0;
} else if (*n == 1) {
d__[1] = dabs(d__[1]);
return 0;
} else if (*n == 2) {
slas2_(&d__[1], &e[1], &d__[2], &sigmn, &sigmx);
d__[1] = sigmx;
d__[2] = sigmn;
return 0;
}
/* Estimate the largest singular value. */
sigmx = 0.f;
i__1 = *n - 1;
for (i__ = 1; i__ <= i__1; ++i__) {
d__[i__] = (r__1 = d__[i__], dabs(r__1));
/* Computing MAX */
r__2 = sigmx, r__3 = (r__1 = e[i__], dabs(r__1));
sigmx = dmax(r__2,r__3);
/* L10: */
}
d__[*n] = (r__1 = d__[*n], dabs(r__1));
/* Early return if SIGMX is zero (matrix is already diagonal). */
if (sigmx == 0.f) {
slasrt_("D", n, &d__[1], &iinfo, (ftnlen)1);
return 0;
}
i__1 = *n;
for (i__ = 1; i__ <= i__1; ++i__) {
/* Computing MAX */
r__1 = sigmx, r__2 = d__[i__];
sigmx = dmax(r__1,r__2);
/* L20: */
}
/* Copy D and E into WORK (in the Z format) and scale (squaring the */
/* input data makes scaling by a power of the radix pointless). */
eps = slamch_("Precision", (ftnlen)9);
safmin = slamch_("Safe minimum", (ftnlen)12);
scale = sqrt(eps / safmin);
scopy_(n, &d__[1], &c__1, &work[1], &c__2);
i__1 = *n - 1;
scopy_(&i__1, &e[1], &c__1, &work[2], &c__2);
i__1 = (*n << 1) - 1;
i__2 = (*n << 1) - 1;
slascl_("G", &c__0, &c__0, &sigmx, &scale, &i__1, &c__1, &work[1], &i__2,
&iinfo, (ftnlen)1);
/* Compute the q's and e's. */
i__1 = (*n << 1) - 1;
for (i__ = 1; i__ <= i__1; ++i__) {
/* Computing 2nd power */
r__1 = work[i__];
work[i__] = r__1 * r__1;
/* L30: */
}
work[*n * 2] = 0.f;
slasq2_(n, &work[1], info);
if (*info == 0) {
i__1 = *n;
for (i__ = 1; i__ <= i__1; ++i__) {
d__[i__] = sqrt(work[i__]);
/* L40: */
}
slascl_("G", &c__0, &c__0, &scale, &sigmx, n, &c__1, &d__[1], n, &
iinfo, (ftnlen)1);
}
return 0;
/* End of SLASQ1 */
} /* slasq1_ */
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