GRASS GIS 8 Programmer's Manual 8.3.2(2024)-exported
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housev.c
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1/* housev.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#include <stdlib.h>
9#include "ccmath.h"
10void housev(double *a, double *d, double *dp, int n)
11{
12 double sc, x, y, h;
13
14 int i, j, k, m, e;
15
16 double *qw, *qs, *pc, *p;
17
18 qs = (double *)calloc(n, sizeof(double));
19 for (j = 0, pc = a; j < n - 2; ++j, pc += n + 1) {
20 m = n - j - 1;
21 for (i = 1, sc = 0.; i <= m; ++i)
22 sc += pc[i] * pc[i];
23 if (sc > 0.) {
24 sc = sqrt(sc);
25 if ((x = *(pc + 1)) < 0.) {
26 y = x - sc;
27 h = 1. / sqrt(-2. * sc * y);
28 }
29 else {
30 y = x + sc;
31 h = 1. / sqrt(2. * sc * y);
32 sc = -sc;
33 }
34 for (i = 0, qw = pc + 1; i < m; ++i) {
35 qs[i] = 0.;
36 if (i)
37 qw[i] *= h;
38 else
39 qw[i] = y * h;
40 }
41 for (i = 0, e = j + 2, p = pc + n + 1, h = 0.; i < m;
42 ++i, p += e++) {
43 qs[i] += (y = qw[i]) * *p++;
44 for (k = i + 1; k < m; ++k) {
45 qs[i] += qw[k] * *p;
46 qs[k] += y * *p++;
47 }
48 h += y * qs[i];
49 }
50 for (i = 0; i < m; ++i) {
51 qs[i] -= h * qw[i];
52 qs[i] += qs[i];
53 }
54 for (i = 0, e = j + 2, p = pc + n + 1; i < m; ++i, p += e++) {
55 for (k = i; k < m; ++k)
56 *p++ -= qw[i] * qs[k] + qs[i] * qw[k];
57 }
58 }
59 d[j] = *pc;
60 dp[j] = sc;
61 }
62 d[j] = *pc;
63 dp[j] = *(pc + 1);
64 d[j + 1] = *(pc += n + 1);
65 free(qs);
66 for (i = 0, m = n + n, p = pc; i < m; ++i)
67 *p-- = 0.;
68 *pc = 1.;
69 *(pc -= n + 1) = 1.;
70 qw = pc - n;
71 for (m = 2; m < n; ++m, qw -= n + 1) {
72 for (j = 0, p = pc, *pc = 1.; j < m; ++j, p += n) {
73 for (i = 0, qs = p, h = 0.; i < m;)
74 h += qw[i++] * *qs++;
75 for (i = 0, qs = p, h += h; i < m;)
76 *qs++ -= h * qw[i++];
77 }
78 for (i = 0, p = qw + m; i < n; ++i)
79 *(--p) = 0.;
80 *(pc -= n + 1) = 1.;
81 }
82}
void housev(double *a, double *d, double *dp, int n)
Definition housev.c:10
#define x