src/sources/utils/algebra.c

   1 #include "sources/utils/algebra.h"
   2 #include <stdlib.h>
   3 #include <math.h>
   4
   5 // small useful function to transform a matrix as given by R
   6 // into a easier-to-handle one.
   7 double* transpose(double* M, int nrow, int ncol)
   8 {
   9     double* Mtr = (double*)malloc(nrow*ncol*sizeof(double));
  10     for (int i=0; i<nrow; i++)
  11     {
  12         for (int j=0; j<ncol; j++)
  13             Mtr[i*ncol+j] = M[i+nrow*j];
  14     }
  15     return Mtr;
  16 }
  17
  18 // auxiliary to compute euclidian norm
  19 double norm2(double* v, int length)
  20 {
  21     double norm = 0.0;
  22     for (int j=0; j<length; j++)
  23         norm += v[j]*v[j];
  24     return sqrt(norm);
  25 }
  26
  27 // auxiliary to compute euclidian distance
  28 double distance2(double* v1, double* v2, int length)
  29 {
  30     double distance = 0.0, diff;
  31     for (int j=0; j<length; j++)
  32     {
  33         diff = v1[j]-v2[j];
  34         distance += diff*diff;
  35     }
  36     return sqrt(distance);
  37 }