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174 lines
4.1 KiB
174 lines
4.1 KiB
#include "clapack.h" |
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/* Subroutine */ int slartg_(real *f, real *g, real *cs, real *sn, real *r__) |
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{ |
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/* System generated locals */ |
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integer i__1; |
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real r__1, r__2; |
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/* Local variables */ |
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integer i__; |
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real f1, g1, eps, scale; |
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integer count; |
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static real safmn2, safmx2; |
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static real safmin; |
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static logical FIRST = TRUE_; |
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/* -- LAPACK auxiliary routine (version 3.2) -- */ |
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/* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. */ |
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/* November 2006 */ |
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/* .. Scalar Arguments .. */ |
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/* .. */ |
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/* Purpose */ |
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/* ======= */ |
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/* SLARTG generate a plane rotation so that */ |
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/* [ CS SN ] . [ F ] = [ R ] where CS**2 + SN**2 = 1. */ |
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/* [ -SN CS ] [ G ] [ 0 ] */ |
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/* This is a slower, more accurate version of the BLAS1 routine SROTG, */ |
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/* with the following other differences: */ |
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/* F and G are unchanged on return. */ |
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/* If G=0, then CS=1 and SN=0. */ |
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/* If F=0 and (G .ne. 0), then CS=0 and SN=1 without doing any */ |
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/* floating point operations (saves work in SBDSQR when */ |
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/* there are zeros on the diagonal). */ |
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/* If F exceeds G in magnitude, CS will be positive. */ |
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/* Arguments */ |
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/* ========= */ |
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/* F (input) REAL */ |
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/* The first component of vector to be rotated. */ |
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/* G (input) REAL */ |
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/* The second component of vector to be rotated. */ |
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/* CS (output) REAL */ |
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/* The cosine of the rotation. */ |
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/* SN (output) REAL */ |
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/* The sine of the rotation. */ |
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/* R (output) REAL */ |
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/* The nonzero component of the rotated vector. */ |
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/* This version has a few statements commented out for thread safety */ |
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/* (machine parameters are computed on each entry). 10 feb 03, SJH. */ |
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/* ===================================================================== */ |
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/* .. Parameters .. */ |
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/* .. */ |
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/* .. Local Scalars .. */ |
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/* LOGICAL FIRST */ |
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/* .. */ |
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/* .. External Functions .. */ |
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/* .. */ |
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/* .. Intrinsic Functions .. */ |
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/* .. */ |
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/* .. Save statement .. */ |
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/* SAVE FIRST, SAFMX2, SAFMIN, SAFMN2 */ |
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/* .. */ |
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/* .. Data statements .. */ |
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/* DATA FIRST / .TRUE. / */ |
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/* .. */ |
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/* .. Executable Statements .. */ |
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if(FIRST) |
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{ |
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safmin = slamch_("S"); |
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eps = slamch_("E"); |
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r__1 = slamch_("B"); |
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i__1 = (integer) (log(safmin / eps) / log(slamch_("B")) / 2.f); |
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safmn2 = pow_ri(&r__1, &i__1); |
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safmx2 = 1.f / safmn2; |
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FIRST = FALSE_; |
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} |
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if (*g == 0.f) { |
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*cs = 1.f; |
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*sn = 0.f; |
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*r__ = *f; |
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} else if (*f == 0.f) { |
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*cs = 0.f; |
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*sn = 1.f; |
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*r__ = *g; |
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} else { |
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f1 = *f; |
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g1 = *g; |
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/* Computing MAX */ |
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r__1 = dabs(f1), r__2 = dabs(g1); |
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scale = dmax(r__1,r__2); |
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if (scale >= safmx2) { |
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count = 0; |
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L10: |
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++count; |
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f1 *= safmn2; |
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g1 *= safmn2; |
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/* Computing MAX */ |
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r__1 = dabs(f1), r__2 = dabs(g1); |
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scale = dmax(r__1,r__2); |
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if (scale >= safmx2) { |
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goto L10; |
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} |
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/* Computing 2nd power */ |
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r__1 = f1; |
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/* Computing 2nd power */ |
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r__2 = g1; |
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*r__ = sqrt(r__1 * r__1 + r__2 * r__2); |
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*cs = f1 / *r__; |
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*sn = g1 / *r__; |
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i__1 = count; |
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for (i__ = 1; i__ <= i__1; ++i__) { |
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*r__ *= safmx2; |
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/* L20: */ |
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} |
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} else if (scale <= safmn2) { |
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count = 0; |
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L30: |
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++count; |
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f1 *= safmx2; |
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g1 *= safmx2; |
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/* Computing MAX */ |
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r__1 = dabs(f1), r__2 = dabs(g1); |
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scale = dmax(r__1,r__2); |
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if (scale <= safmn2) { |
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goto L30; |
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} |
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/* Computing 2nd power */ |
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r__1 = f1; |
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/* Computing 2nd power */ |
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r__2 = g1; |
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*r__ = sqrt(r__1 * r__1 + r__2 * r__2); |
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*cs = f1 / *r__; |
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*sn = g1 / *r__; |
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i__1 = count; |
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for (i__ = 1; i__ <= i__1; ++i__) { |
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*r__ *= safmn2; |
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/* L40: */ |
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} |
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} else { |
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/* Computing 2nd power */ |
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r__1 = f1; |
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/* Computing 2nd power */ |
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r__2 = g1; |
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*r__ = sqrt(r__1 * r__1 + r__2 * r__2); |
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*cs = f1 / *r__; |
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*sn = g1 / *r__; |
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} |
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if (dabs(*f) > dabs(*g) && *cs < 0.f) { |
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*cs = -(*cs); |
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*sn = -(*sn); |
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*r__ = -(*r__); |
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} |
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} |
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return 0; |
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/* End of SLARTG */ |
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} /* slartg_ */
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