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/* Copyright (C) 2017 - IIT Bombay - FOSSEE
This file must be used under the terms of the CeCILL.
This source file is licensed as described in the file COPYING, which
you should have received as part of this distribution. The terms
are also available at
http://www.cecill.info/licences/Licence_CeCILL_V2-en.txt
Organization: FOSSEE, IIT Bombay
Author: Brijesh Gupta C R
Email: toolbox@scilab.in
*/
#include <stdio.h>
#include "math.h"
#include "besselk.h"
#define ACC 40.0
#define BIGNO 1.0e10
#define BIGNI 1.0e-10
static float fbessi0( float x )
{
float ax,ans;
float y;
if ((ax=fabs(x)) < 3.75) {
y=x/3.75,y=y*y;
ans=1.0+y*(3.5156229+y*(3.0899424+y*(1.2067492
+y*(0.2659732+y*(0.360768e-1+y*0.45813e-2)))));
} else {
y=3.75/ax;
ans=(exp(ax)/sqrt(ax))*(0.39894228+y*(0.1328592e-1
+y*(0.225319e-2+y*(-0.157565e-2+y*(0.916281e-2
+y*(-0.2057706e-1+y*(0.2635537e-1+y*(-0.1647633e-1
+y*0.392377e-2))))))));
}
return ans;
}
static float fbessi1( float x)
{
float ax,ans;
float y;
if ((ax=fabs(x)) < 3.75) {
y=x/3.75,y=y*y;
ans=ax*(0.5+y*(0.87890594+y*(0.51498869+y*(0.15084934
+y*(0.2658733e-1+y*(0.301532e-2+y*0.32411e-3))))));
} else {
y=3.75/ax;
ans=0.2282967e-1+y*(-0.2895312e-1+y*(0.1787654e-1
-y*0.420059e-2));
ans=0.39894228+y*(-0.3988024e-1+y*(-0.362018e-2
+y*(0.163801e-2+y*(-0.1031555e-1+y*ans))));
ans *= (exp(ax)/sqrt(ax));
}
return x < 0.0 ? -ans : ans;
}
static float fbessk0( float x )
{
float y,ans;
if (x <= 2.0) {
y=x*x/4.0;
ans=(-log(x/2.0)*fbessi0(x))+(-0.57721566+y*(0.42278420
+y*(0.23069756+y*(0.3488590e-1+y*(0.262698e-2
+y*(0.10750e-3+y*0.74e-5))))));
} else {
y=2.0/x;
ans=(exp(-x)/sqrt(x))*(1.25331414+y*(-0.7832358e-1
+y*(0.2189568e-1+y*(-0.1062446e-1+y*(0.587872e-2
+y*(-0.251540e-2+y*0.53208e-3))))));
}
return ans;
}
static float fbessk1( float x )
{
float y,ans;
if (x <= 2.0) {
y=x*x/4.0;
ans=(log(x/2.0)*fbessi1(x))+(1.0/x)*(1.0+y*(0.15443144
+y*(-0.67278579+y*(-0.18156897+y*(-0.1919402e-1
+y*(-0.110404e-2+y*(-0.4686e-4)))))));
} else {
y=2.0/x;
ans=(exp(-x)/sqrt(x))*(1.25331414+y*(0.23498619
+y*(-0.3655620e-1+y*(0.1504268e-1+y*(-0.780353e-2
+y*(0.325614e-2+y*(-0.68245e-3)))))));
}
return ans;
}
float fbessk( int n, float x )
{
int j;
float bk,bkm,bkp,tox;
if (n < 0 || x == 0.0)
{
float dblank;
return( dblank );
}
if (n == 0)
return( fbessk0(x) );
if (n == 1)
return( fbessk1(x) );
tox=2.0/x;
bkm=fbessk0(x);
bk=fbessk1(x);
for (j=1;j<n;j++) {
bkp=bkm+j*tox*bk;
bkm=bk;
bk=bkp;
}
return bk;
}
void sbesselka(float* inp1,int size1, float* inp2,int size2, float* oup)
{
int i;
if(size1 != size2)
printf("Error! arguments #1 and #2 have incompatible dimensions.");
for(i = 0; i<size1;i++)
{
oup[i] = fbessk(inp1[i],inp2[i]);
}
}
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