#include <math.h>
#include <gsl/gsl_matrix.h>

#include "kernels.h"

/* estimation of sqrt(3) */
#define SQRT3 1.73205080757

int squared_exp ( double sigmaf, double ell, gsl_matrix *A, gsl_matrix *B, 
    gsl_matrix *result ) 
{
  int i, j, n = A->size2, m = B->size2;
  /* ensure that the matrix result is the same size as the matrixs */
  if ( result->size1 != n || result->size2 != m )
    return 1;

  gsl_matrix_set_zero(result);
  double r, rval, x, y;
  for ( i = 0 ; i < n ; i++ ) {
    for ( j = 0 ; j < m ; j++ ) {
      x = gsl_matrix_get(A, 0, i);
      y = gsl_matrix_get(B, 0, j);

      r = sqrt((x - y)*(x - y));
      rval = sigmaf*sigmaf*exp(-(r*r)/(2*ell*ell));
      gsl_matrix_set(result, i, j, rval);
    }
  }

  return 0;
}

int matern32 ( double sigmaf, double ell, gsl_matrix *A, gsl_matrix *B, 
    gsl_matrix *result ) 
{
  int i, j, n = A->size2, m = B->size2;
  /* ensure that the matrix result is the same size as the matrixs */
  if ( result->size1 != n || result->size2 != m )
    return 1;

  double r, rval, x, y;
  for ( i = 0 ; i < n ; i++ ) {
    for ( j = 0 ; j < m ; j++ ) {
      x = gsl_matrix_get(A, 0, i);
      y = gsl_matrix_get(B, 0, j);

      r = sqrt((x - y)*(x - y));
      /* sigmaf^2*(1+sqrt(3)*r/ell)*exp(-sqrt(3)*r/ell) */
      rval = sigmaf*sigmaf*(1+SQRT3*r/ell)*exp(-SQRT3*r/ell);
      gsl_matrix_set(result, i, j, rval);
    }
  }

  return 0;
}