GRASS GIS 7 Programmer's Manual  7.5.svn(2018)-r72996
svdval.c
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1 /* svdval.c CCMATH mathematics library source code.
2  *
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"
10 int svdval(double *d, double *a, int m, int n)
11 {
12  double *p, *p1, *q, *w, *v;
13
14  double s, h, u;
15
16  int i, j, k, mm, nm, ms;
17
18  if (m < n)
19  return -1;
20  w = (double *)calloc(m, sizeof(double));
21  for (i = 0, mm = m, nm = n - 1, p = a; i < n; ++i, --mm, --nm, p += n + 1) {
22  if (mm > 1) {
23  for (j = 0, q = p, s = 0.; j < mm; ++j, q += n) {
24  w[j] = *q;
25  s += *q * *q;
26  }
27  if (s > 0.) {
28  h = sqrt(s);
29  if (*p < 0.)
30  h = -h;
31  s += *p * h;
32  s = 1. / s;
33  w[0] += h;
34  for (k = 1, ms = n - i; k < ms; ++k) {
35  for (j = 0, q = p + k, u = 0.; j < mm; q += n)
36  u += w[j++] * *q;
37  u *= s;
38  for (j = 0, q = p + k; j < mm; q += n)
39  *q -= u * w[j++];
40  }
41  *p = -h;
42  }
43  }
44  p1 = p + 1;
45  if (nm > 1) {
46  for (j = 0, q = p1, s = 0.; j < nm; ++j, ++q)
47  s += *q * *q;
48  if (s > 0.) {
49  h = sqrt(s);
50  if (*p1 < 0.)
51  h = -h;
52  s += *p1 * h;
53  s = 1. / s;
54  *p1 += h;
55  for (k = n, ms = n * (m - i); k < ms; k += n) {
56  for (j = 0, q = p1, v = p1 + k, u = 0.; j < nm; ++j)
57  u += *q++ * *v++;
58  u *= s;
59  for (j = 0, q = p1, v = p1 + k; j < nm; ++j)
60  *v++ -= u * *q++;
61  }
62  *p1 = -h;
63  }
64  }
65  }
66
67  for (j = 0, p = a; j < n; ++j, p += n + 1) {
68  d[j] = *p;
69  if (j != n - 1)
70  w[j] = *(p + 1);
71  else
72  w[j] = 0.;
73  }
74  qrbdi(d, w, n);
75  for (i = 0; i < n; ++i)
76  if (d[i] < 0.)
77  d[i] = -d[i];
78  free(w);
79  return 0;
80 }
int svdval(double *d, double *a, int m, int n)
Definition: svdval.c:10
void free(void *)
int qrbdi(double *d, double *e, int n)
Definition: qrbdi.c:9