legendre.c
/*
* Copyright (c) 2002, 2017 Jens Keiner, Stefan Kunis, Daniel Potts
*
* This program is free software; you can redistribute it and/or modify it under
* the terms of the GNU General Public License as published by the Free Software
* Foundation; either version 2 of the License, or (at your option) any later
* version.
*
* This program is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
* FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
* details.
*
* You should have received a copy of the GNU General Public License along with
* this program; if not, write to the Free Software Foundation, Inc., 51
* Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*/
#include <math.h>
#include <stdio.h>
#include "infft.h"
#include "legendre.h"
#include "infft.h"
/* One over sqrt(pi) */
DK(KSQRTPII,0.56418958354775628694807945156077258584405062932900);
static inline R alpha_al(const int k, const int n)
{
if (k > 0)
{
if (k < n)
return IF(k%2,K(1.0),K(-1.0));
else
return SQRT(((R)(2*k+1))/((R)(k-n+1)))*SQRT((((R)(2*k+1))/((R)(k+n+1))));
}
else if (k == 0)
{
if (n == 0)
return K(1.0);
else
return IF(n%2,K(0.0),K(-1.0));
}
return K(0.0);
}
static inline R beta_al(const int k, const int n)
{
if (0 <= k && k < n)
return K(1.0);
else
return K(0.0);
}
static inline R gamma_al(const int k, const int n)
{
if (k == -1)
return SQRT(KSQRTPII*nfft_lambda((R)(n),K(0.5)));
else if (k <= n)
return K(0.0);
else
return -SQRT(((R)(k-n))/((R)(k-n+1))*((R)(k+n))/((R)(k+n+1)));
}
void alpha_al_row(R *alpha, const int N, const int n)
{
int j;
R *p = alpha;
for (j = -1; j <= N; j++)
*p++ = alpha_al(j,n);
}
void beta_al_row(R *beta, const int N, const int n)
{
int j;
R *p = beta;
for (j = -1; j <= N; j++)
*p++ = beta_al(j,n);
}
void gamma_al_row(R *gamma, const int N, const int n)
{
int j;
R *p = gamma;
for (j = -1; j <= N; j++)
*p++ = gamma_al(j,n);
}
inline void alpha_al_all(R *alpha, const int N)
{
int i,j;
R *p = alpha;
for (i = 0; i <= N; i++)
for (j = -1; j <= N; j++)
*p++ = alpha_al(j,i);
}
inline void beta_al_all(R *alpha, const int N)
{
int i,j;
R *p = alpha;
for (i = 0; i <= N; i++)
for (j = -1; j <= N; j++)
*p++ = beta_al(j,i);
}
inline void gamma_al_all(R *alpha, const int N)
{
int i,j;
R *p = alpha;
for (i = 0; i <= N; i++)
for (j = -1; j <= N; j++)
*p++ = gamma_al(j,i);
}
void eval_al(R *x, R *y, const int size, const int k, R *alpha,
R *beta, R *gamma)
{
/* Evaluate the associated Legendre polynomial P_{k,nleg} (l,x) for the vector
* of knots x[0], ..., x[size-1] by the Clenshaw algorithm
*/
int i,j;
R a,b,x_val_act,a_old;
R *x_act, *y_act;
R *alpha_act, *beta_act, *gamma_act;
/* Traverse all nodes. */
x_act = x;
y_act = y;
for (i = 0; i < size; i++)
{
a = 1.0;
b = 0.0;
x_val_act = *x_act;
if (k == 0)
{
*y_act = 1.0;
}
else
{
alpha_act = &(alpha[k]);
beta_act = &(beta[k]);
gamma_act = &(gamma[k]);
for (j = k; j > 1; j--)
{
a_old = a;
a = b + a_old*((*alpha_act)*x_val_act+(*beta_act));
b = a_old*(*gamma_act);
alpha_act--;
beta_act--;
gamma_act--;
}
*y_act = (a*((*alpha_act)*x_val_act+(*beta_act))+b);
}
x_act++;
y_act++;
}
}
int eval_al_thresh(R *x, R *y, const int size, const int k, R *alpha,
R *beta, R *gamma, R threshold)
{
/* Evaluate the associated Legendre polynomial P_{k,nleg} (l,x) for the vector
* of knots x[0], ..., x[size-1] by the Clenshaw algorithm
*/
int i,j;
R a,b,x_val_act,a_old;
R *x_act, *y_act;
R *alpha_act, *beta_act, *gamma_act;
/* Traverse all nodes. */
x_act = x;
y_act = y;
for (i = 0; i < size; i++)
{
a = 1.0;
b = 0.0;
x_val_act = *x_act;
if (k == 0)
{
*y_act = 1.0;
}
else
{
alpha_act = &(alpha[k]);
beta_act = &(beta[k]);
gamma_act = &(gamma[k]);
for (j = k; j > 1; j--)
{
a_old = a;
a = b + a_old*((*alpha_act)*x_val_act+(*beta_act));
b = a_old*(*gamma_act);
alpha_act--;
beta_act--;
gamma_act--;
}
*y_act = (a*((*alpha_act)*x_val_act+(*beta_act))+b);
if (fabs(*y_act) > threshold)
{
return 1;
}
}
x_act++;
y_act++;
}
return 0;
}
alpha_al_all
void alpha_al_all(R *alpha, const int N)
Compute three-term-recurrence coefficients of associated Legendre functions for .
Definition: legendre.c:89
eval_al_thresh
int eval_al_thresh(R *x, R *y, const int size, const int k, R *alpha, R *beta, R *gamma, R threshold)
Evaluates an associated Legendre polynomials using the Clenshaw-algorithm if it no exceeds a given t...
Definition: legendre.c:161
beta_al_all
void beta_al_all(R *alpha, const int N)
Compute three-term-recurrence coefficients of associated Legendre functions for .
Definition: legendre.c:98
gamma_al_all
void gamma_al_all(R *alpha, const int N)
Compute three-term-recurrence coefficients of associated Legendre functions for .
Definition: legendre.c:107
eval_al
void eval_al(R *x, R *y, const int size, const int k, R *alpha, R *beta, R *gamma)
Evaluates an associated Legendre polynomials using the Clenshaw-algorithm.
Definition: legendre.c:116