GRASS GIS 8 Programmer's Manual 8.4.1(2025)-45ca3179ab
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chouse.c
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1/* chouse.c CCMATH mathematics library source code.
2 *
3 * Copyright (C) 2000 Daniel A. Atkinson All rights reserved.
4 * This code may be redistributed under the terms of the GNU library
5 * public license (LGPL). ( See the lgpl.license file for details.)
6 * ------------------------------------------------------------------------
7 */
8
9#include <stdlib.h>
10#include "ccmath.h"
11
12void chouse(Cpx *a, double *d, double *dp, int n)
13{
14 double sc, x, y;
15
16 Cpx cc, u, *q0;
17
18 int i, j, k, m, e;
19
20 Cpx *qw, *pc, *p;
21
22 q0 = (Cpx *)calloc(2 * n, sizeof(Cpx));
23 for (i = 0, p = q0 + n, pc = a; i < n; ++i, pc += n + 1)
24 *p++ = *pc;
25 for (j = 0, pc = a; j < n - 2; ++j, pc += n + 1) {
26 m = n - j - 1;
27 for (i = 1, sc = 0.; i <= m; ++i)
28 sc += pc[i].re * pc[i].re + pc[i].im * pc[i].im;
29 if (sc > 0.) {
30 sc = sqrt(sc);
31 p = pc + 1;
32 y = sc + (x = sqrt(p->re * p->re + p->im * p->im));
33 if (x > 0.) {
34 cc.re = p->re / x;
35 cc.im = p->im / x;
36 }
37 else {
38 cc.re = 1.;
39 cc.im = 0.;
40 }
41 x = 1. / sqrt(2. * sc * y);
42 y *= x;
43 for (i = 0, qw = pc + 1; i < m; ++i) {
44 q0[i].re = q0[i].im = 0.;
45 if (i) {
46 qw[i].re *= x;
47 qw[i].im *= -x;
48 }
49 else {
50 qw[0].re = y * cc.re;
51 qw[0].im = -y * cc.im;
52 }
53 }
54 for (i = 0, e = j + 2, p = pc + n + 1, y = 0.; i < m;
55 ++i, p += e++) {
56 q0[i].re +=
57 (u.re = qw[i].re) * p->re - (u.im = qw[i].im) * p->im;
58 q0[i].im += u.re * p->im + u.im * p->re;
59 ++p;
60 for (k = i + 1; k < m; ++k, ++p) {
61 q0[i].re += qw[k].re * p->re - qw[k].im * p->im;
62 q0[i].im += qw[k].im * p->re + qw[k].re * p->im;
63 q0[k].re += u.re * p->re + u.im * p->im;
64 q0[k].im += u.im * p->re - u.re * p->im;
65 }
66 y += u.re * q0[i].re + u.im * q0[i].im;
67 }
68 for (i = 0; i < m; ++i) {
69 q0[i].re -= y * qw[i].re;
70 q0[i].re += q0[i].re;
71 q0[i].im -= y * qw[i].im;
72 q0[i].im += q0[i].im;
73 }
74 for (i = 0, e = j + 2, p = pc + n + 1; i < m; ++i, p += e++) {
75 for (k = i; k < m; ++k, ++p) {
76 p->re -= qw[i].re * q0[k].re + qw[i].im * q0[k].im +
77 q0[i].re * qw[k].re + q0[i].im * qw[k].im;
78 p->im -= qw[i].im * q0[k].re - qw[i].re * q0[k].im +
79 q0[i].im * qw[k].re - q0[i].re * qw[k].im;
80 }
81 }
82 }
83 d[j] = pc->re;
84 dp[j] = sc;
85 }
86 d[j] = pc->re;
87 d[j + 1] = (pc + n + 1)->re;
88 u = *(pc + 1);
89 dp[j] = sqrt(u.re * u.re + u.im * u.im);
90 for (j = 0, pc = a, qw = q0 + n; j < n; ++j, pc += n + 1) {
91 *pc = qw[j];
92 for (i = 1, p = pc + n; i < n - j; ++i, p += n) {
93 pc[i].re = p->re;
94 pc[i].im = -p->im;
95 }
96 }
97 free(q0);
98}
struct complex Cpx
Definition ccmath.h:41
void chouse(Cpx *a, double *d, double *dp, int n)
Definition chouse.c:12
double re
Definition ccmath.h:39
double im
Definition ccmath.h:39
#define x