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/* taken from i.pca */
#include <stdlib.h>
#include <grass/gmath.h>
#include <grass/gis.h>
static int egcmp(const void *pa, const void *pb);
/*!
* \fn int eigen (double **M, double **Vectors, double *lambda, int n)
*
* \brief Computes eigenvalues (and eigen vectors if desired) for
* symmetric matices.
*
* Computes eigenvalues (and eigen vectors if desired) for symmetric matices.
*
* \param M Input matrix
* \param Vectors eigen output vector matrix
* \param lambda Output eigenvalues
* \param n Input matrix dimension
* \return int
*/
int eigen(double **M, /* Input matrix */
double **Vectors, /* eigen vector matrix -output */
double *lambda, /* Output eigenvalues */
int n /* Input matrix dimension */
)
{
int i, j;
double **a, *e;
a = G_alloc_matrix(n, n);
e = G_alloc_vector(n);
for (i = 0; i < n; i++)
for (j = 0; j < n; j++)
a[i][j] = M[i][j];
G_tred2(a, n, lambda, e);
G_tqli(lambda, e, n, a);
/* Returns eigenvectors */
if (Vectors)
for (i = 0; i < n; i++)
for (j = 0; j < n; j++)
Vectors[i][j] = a[i][j];
G_free_matrix(a);
G_free_vector(e);
return 0;
}
/*!
* \fn int egvorder2 (double *d, double **z, long bands)
*
* \brief
*
* Returns 0.
*
* \param d
* \param z
* \param bands
* \return int
*/
int egvorder2(double *d, double **z, long bands)
{
double *buff;
double **tmp;
int i, j;
/* allocate temporary matrix */
buff = (double *)G_malloc(bands * (bands + 1) * sizeof(double));
tmp = (double **)G_malloc(bands * sizeof(double *));
for (i = 0; i < bands; i++)
tmp[i] = &buff[i * (bands + 1)];
/* concatenate (vertically) z and d into tmp */
for (i = 0; i < bands; i++) {
for (j = 0; j < bands; j++)
tmp[i][j + 1] = z[j][i];
tmp[i][0] = d[i];
}
/* sort the combined matrix */
qsort(tmp, bands, sizeof(double *), egcmp);
/* split tmp into z and d */
for (i = 0; i < bands; i++) {
for (j = 0; j < bands; j++)
z[j][i] = tmp[i][j + 1];
d[i] = tmp[i][0];
}
/* free temporary matrix */
G_free(tmp);
G_free(buff);
return 0;
}
/*!
* \fn int transpose2 (double **eigmat, long bands)
*
* \brief
*
* Returns 0.
*
* \param eigmat
* \param bands
* \return int
*/
int transpose2(double **eigmat, long bands)
{
int i, j;
for (i = 0; i < bands; i++)
for (j = 0; j < i; j++) {
double tmp = eigmat[i][j];
eigmat[i][j] = eigmat[j][i];
eigmat[j][i] = tmp;
}
return 0;
}
static int egcmp(const void *pa, const void *pb)
{
const double *a = *(const double *const *)pa;
const double *b = *(const double *const *)pb;
if (*a > *b)
return -1;
if (*a < *b)
return 1;
return 0;
}
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