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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
Author: Ankit Raj
Organization: FOSSEE, IIT Bombay
Email: toolbox@scilab.in
*/
#include<stdio.h>
#include<math.h>
#include "amell.h"
#define N 30
#define DBL_EPSILON 2.2204460492503131E-16
double damells(double u,double x)
{
double a[N+1];
double g[N+1];
double c[N+1];
double two_n;
double phi;
double k;
int n;
k=(long double)fabs(x);
if(k==1.0)
return 0;
if(k>1.0)
printf("Wrong type of input argument type #2");
a[0]=1.0;
g[0]=sqrt(1.0-k*k);
c[0]=k;
two_n=1.0;
for(n=0;n<N;n++)
{
if(fabs(a[n]-g[n])<(a[n]*DBL_EPSILON))
{
break;
}
two_n+=two_n;
a[n+1]=0.5*(a[n]+g[n]);
g[n+1]=sqrt(a[n]*g[n]);
c[n+1]=0.5*(a[n]-g[n]);
}
phi=two_n*a[n]*u;
for(;n>0;n--)
{
phi=0.5*(phi+asin(c[n]*sin(phi)/a[n]));
}
return (double)phi;
}
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