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/* claev2.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 claev2_(complex *a, complex *b, complex *c__, real *rt1,
real *rt2, real *cs1, complex *sn1)
{
/* System generated locals */
real r__1, r__2, r__3;
complex q__1, q__2;
/* Builtin functions */
double c_abs(complex *);
void r_cnjg(complex *, complex *);
/* Local variables */
real t;
complex w;
extern /* Subroutine */ int slaev2_(real *, real *, real *, real *, real *
, real *, real *);
/* -- LAPACK auxiliary routine (version 3.2) -- */
/* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. */
/* November 2006 */
/* .. Scalar Arguments .. */
/* .. */
/* Purpose */
/* ======= */
/* CLAEV2 computes the eigendecomposition of a 2-by-2 Hermitian matrix */
/* [ A B ] */
/* [ CONJG(B) C ]. */
/* On return, RT1 is the eigenvalue of larger absolute value, RT2 is the */
/* eigenvalue of smaller absolute value, and (CS1,SN1) is the unit right */
/* eigenvector for RT1, giving the decomposition */
/* [ CS1 CONJG(SN1) ] [ A B ] [ CS1 -CONJG(SN1) ] = [ RT1 0 ] */
/* [-SN1 CS1 ] [ CONJG(B) C ] [ SN1 CS1 ] [ 0 RT2 ]. */
/* Arguments */
/* ========= */
/* A (input) COMPLEX */
/* The (1,1) element of the 2-by-2 matrix. */
/* B (input) COMPLEX */
/* The (1,2) element and the conjugate of the (2,1) element of */
/* the 2-by-2 matrix. */
/* C (input) COMPLEX */
/* The (2,2) element of the 2-by-2 matrix. */
/* RT1 (output) REAL */
/* The eigenvalue of larger absolute value. */
/* RT2 (output) REAL */
/* The eigenvalue of smaller absolute value. */
/* CS1 (output) REAL */
/* SN1 (output) COMPLEX */
/* The vector (CS1, SN1) is a unit right eigenvector for RT1. */
/* Further Details */
/* =============== */
/* RT1 is accurate to a few ulps barring over/underflow. */
/* RT2 may be inaccurate if there is massive cancellation in the */
/* determinant A*C-B*B; higher precision or correctly rounded or */
/* correctly truncated arithmetic would be needed to compute RT2 */
/* accurately in all cases. */
/* CS1 and SN1 are accurate to a few ulps barring over/underflow. */
/* Overflow is possible only if RT1 is within a factor of 5 of overflow. */
/* Underflow is harmless if the input data is 0 or exceeds */
/* underflow_threshold / macheps. */
/* ===================================================================== */
/* .. Parameters .. */
/* .. */
/* .. Local Scalars .. */
/* .. */
/* .. External Subroutines .. */
/* .. */
/* .. Intrinsic Functions .. */
/* .. */
/* .. Executable Statements .. */
if (c_abs(b) == 0.f) {
w.r = 1.f, w.i = 0.f;
} else {
r_cnjg(&q__2, b);
r__1 = c_abs(b);
q__1.r = q__2.r / r__1, q__1.i = q__2.i / r__1;
w.r = q__1.r, w.i = q__1.i;
}
r__1 = a->r;
r__2 = c_abs(b);
r__3 = c__->r;
slaev2_(&r__1, &r__2, &r__3, rt1, rt2, cs1, &t);
q__1.r = t * w.r, q__1.i = t * w.i;
sn1->r = q__1.r, sn1->i = q__1.i;
return 0;
/* End of CLAEV2 */
} /* claev2_ */
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