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/* slaqr1.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 slaqr1_(integer *n, real *h__, integer *ldh, real *sr1,
real *si1, real *sr2, real *si2, real *v)
{
/* System generated locals */
integer h_dim1, h_offset;
real r__1, r__2, r__3;
/* Local variables */
real s, h21s, h31s;
/* -- LAPACK auxiliary routine (version 3.2) -- */
/* Univ. of Tennessee, Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd.. */
/* November 2006 */
/* .. Scalar Arguments .. */
/* .. */
/* .. Array Arguments .. */
/* .. */
/* Given a 2-by-2 or 3-by-3 matrix H, SLAQR1 sets v to a */
/* scalar multiple of the first column of the product */
/* (*) K = (H - (sr1 + i*si1)*I)*(H - (sr2 + i*si2)*I) */
/* scaling to avoid overflows and most underflows. It */
/* is assumed that either */
/* 1) sr1 = sr2 and si1 = -si2 */
/* or */
/* 2) si1 = si2 = 0. */
/* This is useful for starting double implicit shift bulges */
/* in the QR algorithm. */
/* N (input) integer */
/* Order of the matrix H. N must be either 2 or 3. */
/* H (input) REAL array of dimension (LDH,N) */
/* The 2-by-2 or 3-by-3 matrix H in (*). */
/* LDH (input) integer */
/* The leading dimension of H as declared in */
/* the calling procedure. LDH.GE.N */
/* SR1 (input) REAL */
/* SI1 The shifts in (*). */
/* SR2 */
/* SI2 */
/* V (output) REAL array of dimension N */
/* A scalar multiple of the first column of the */
/* matrix K in (*). */
/* ================================================================ */
/* Based on contributions by */
/* Karen Braman and Ralph Byers, Department of Mathematics, */
/* University of Kansas, USA */
/* ================================================================ */
/* .. Parameters .. */
/* .. */
/* .. Local Scalars .. */
/* .. */
/* .. Intrinsic Functions .. */
/* .. */
/* .. Executable Statements .. */
/* Parameter adjustments */
h_dim1 = *ldh;
h_offset = 1 + h_dim1;
h__ -= h_offset;
--v;
/* Function Body */
if (*n == 2) {
s = (r__1 = h__[h_dim1 + 1] - *sr2, dabs(r__1)) + dabs(*si2) + (r__2 =
h__[h_dim1 + 2], dabs(r__2));
if (s == 0.f) {
v[1] = 0.f;
v[2] = 0.f;
} else {
h21s = h__[h_dim1 + 2] / s;
v[1] = h21s * h__[(h_dim1 << 1) + 1] + (h__[h_dim1 + 1] - *sr1) *
((h__[h_dim1 + 1] - *sr2) / s) - *si1 * (*si2 / s);
v[2] = h21s * (h__[h_dim1 + 1] + h__[(h_dim1 << 1) + 2] - *sr1 - *
sr2);
}
} else {
s = (r__1 = h__[h_dim1 + 1] - *sr2, dabs(r__1)) + dabs(*si2) + (r__2 =
h__[h_dim1 + 2], dabs(r__2)) + (r__3 = h__[h_dim1 + 3], dabs(
r__3));
if (s == 0.f) {
v[1] = 0.f;
v[2] = 0.f;
v[3] = 0.f;
} else {
h21s = h__[h_dim1 + 2] / s;
h31s = h__[h_dim1 + 3] / s;
v[1] = (h__[h_dim1 + 1] - *sr1) * ((h__[h_dim1 + 1] - *sr2) / s)
- *si1 * (*si2 / s) + h__[(h_dim1 << 1) + 1] * h21s + h__[
h_dim1 * 3 + 1] * h31s;
v[2] = h21s * (h__[h_dim1 + 1] + h__[(h_dim1 << 1) + 2] - *sr1 - *
sr2) + h__[h_dim1 * 3 + 2] * h31s;
v[3] = h31s * (h__[h_dim1 + 1] + h__[h_dim1 * 3 + 3] - *sr1 - *
sr2) + h21s * h__[(h_dim1 << 1) + 3];
}
}
return 0;
} /* slaqr1_ */
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