GRASS GIS 7 Programmer's Manual  7.5.svn(2017)-r71790
house.c
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1 /* house.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 void house(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(2 * n, sizeof(double));
19  for (j = 0, qw = qs + n, pc = a; j < n; pc += n + 1)
20  qw[j++] = *pc;
21  for (j = 0, pc = a; j < n - 2; ++j, pc += n + 1) {
22  m = n - j - 1;
23  for (i = 1, sc = 0.; i <= m; ++i)
24  sc += pc[i] * pc[i];
25  if (sc > 0.) {
26  sc = sqrt(sc);
27  if ((x = *(pc + 1)) < 0.) {
28  y = x - sc;
29  h = 1. / sqrt(-2. * sc * y);
30  }
31  else {
32  y = x + sc;
33  h = 1. / sqrt(2. * sc * y);
34  sc = -sc;
35  }
36  for (i = 0, qw = pc + 1; i < m; ++i) {
37  qs[i] = 0.;
38  if (i)
39  qw[i] *= h;
40  else
41  qw[i] = y * h;
42  }
43  for (i = 0, e = j + 2, p = pc + n + 1, h = 0.; i < m;
44  ++i, p += e++) {
45  qs[i] += (y = qw[i]) * *p++;
46  for (k = i + 1; k < m; ++k) {
47  qs[i] += qw[k] * *p;
48  qs[k] += y * *p++;
49  }
50  h += y * qs[i];
51  }
52  for (i = 0; i < m; ++i) {
53  qs[i] -= h * qw[i];
54  qs[i] += qs[i];
55  }
56  for (i = 0, e = j + 2, p = pc + n + 1; i < m; ++i, p += e++) {
57  for (k = i; k < m; ++k)
58  *p++ -= qw[i] * qs[k] + qs[i] * qw[k];
59  }
60  }
61  d[j] = *pc;
62  dp[j] = sc;
63  }
64  d[j] = *pc;
65  dp[j] = *(pc + 1);
66  d[j + 1] = *(pc + n + 1);
67  for (j = 0, pc = a, qw = qs + n; j < n; ++j, pc += n + 1) {
68  *pc = qw[j];
69  for (i = 1, p = pc + n; i < n - j; p += n)
70  pc[i++] = *p;
71  }
72  free(qs);
73 }
void free(void *)
#define x
void house(double *a, double *d, double *ud, int n)
Definition: house.c:10