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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 "besseli.h"
#define ACC 40.0
#define BIGNO 1.0e10
#define BIGNI 1.0e-10
double onebessi( double inp1, double inp2)
{
int j;
double bi,bim,bip,tox,result,s,res,t;
if (inp1 < 0)
{
double dblank;
return( dblank );
}
if (inp1 == 0)
{
if ((s=fabs(inp2)) < 3.75)
{
t=inp2/3.75,t=t*t;
res=1.0+t*(3.5156229+t*(3.0899424+t*(1.2067492+t*(0.2659732+t*(0.360768e-1+t*0.45813e-2)))));
}
else
{
t=3.75/s;
res=(exp(s)/sqrt(s))*(0.39894228+t*(0.1328592e-1+t*(0.225319e-2+t*(-0.157565e-2+t*(0.916281e-2+t*(-0.2057706e-1+t*(0.2635537e-1+t*(-0.1647633e-1+t*0.392377e-2))))))));
}
return res;
}
if (inp1 == 1)
{
if ((s=fabs(inp2)) < 3.75)
{
t=inp2/3.75,t=t*t;
res=s*(0.5+t*(0.87890594+t*(0.51498869+t*(0.15084934+t*(0.2658733e-1+t*(0.301532e-2+t*0.32411e-3))))));
}
else
{
t=3.75/s;
res=0.2282967e-1+t*(-0.2895312e-1+t*(0.1787654e-1-t*0.420059e-2));
res=0.39894228+t*(-0.3988024e-1+t*(-0.362018e-2+t*(0.163801e-2+t*(-0.1031555e-1+t*res))));
res *= (exp(s)/sqrt(s));
}
return inp2 < 0.0 ? -res : res;
}
if (inp2 == 0.0)
return 0.0;
else
{
tox=2.0/fabs(inp2);
bip=result=0.0;
bi=1.0;
for (j=2*(inp1+(int) sqrt(ACC*inp1));j>0;j--)
{
bim=bip+j*tox*bi;
bip=bi;
bi=bim;
if (fabs(bi) > BIGNO)
{
result *= BIGNI;
bi *= BIGNI;
bip *= BIGNI;
}
if (j == inp1) result=bip;
}
if ((s=fabs(inp2)) < 3.75)
{
t=inp2/3.75,t=t*t;
res=1.0+t*(3.5156229+t*(3.0899424+t*(1.2067492+t*(0.2659732+t*(0.360768e-1+t*0.45813e-2)))));
}
else
{
t=3.75/s;
res=(exp(s)/sqrt(s))*(0.39894228+t*(0.1328592e-1+t*(0.225319e-2+t*(-0.157565e-2+t*(0.916281e-2+t*(-0.2057706e-1+t*(0.2635537e-1+t*(-0.1647633e-1+t*0.392377e-2))))))));
}
result *= res/bi;
return inp2 < 0.0 && (int)inp1%2 == 1 ? -result : result;
}
}
void dbesselia(double* inp1,int size1, double* inp2,int size2, double* oup)
{
int i;
if(size1 != size2)
printf("Error! arguments #1 and #2 have incompatible dimensions.");
for(i = 0; i<size1;i++)
{
oup[i] = onebessi(inp1[i],inp2[i]);
}
}
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