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/* Copyright (C) 2016 - 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: Brijesh Gupta C R
Organization: FOSSEE, IIT Bombay
Email: toolbox@scilab.in
*/
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include "erfinv.h"
# define PI 3.1415927
double derfinvs (double inp1)
{
double a[] = {0.88622692374517353,-1.6601283962374516,0.92661860147244357,-0.14110320437680104}; //Coefficients for the formula to calculate inverse error
double b[] = {-2.13505380615258078,1.46060340345661088,-0.33198239813321595,0.01197270616590528}; //Coefficients for the formula to calculate inverse error
double c[] = {-1.994216456587148,-1.87267416351196,3.60874665878559364,1.82365845766309853}; //Coefficients for the formula to calculate inverse error
double d[] = {3.74146294065960872,1.81848952562894617}; //Coefficients for the formula to calculate inverse error
if ((inp1 > 1) || (inp1 < -1))
{
return 0.0/0.0; // returns Nan
}
if ((inp1 >= -0.7) && (inp1 <= 0.7))
{
double sq = inp1 * inp1;
return (inp1 * (((a[3]*sq+a[2]) * sq+a[1]) * sq+a[0]) / ((((b[3]*sq+b[2]) * sq+b[1]) * sq+b[0]) * sq+1)); //Inverse error formula
}
else if ((inp1 > 0.7) && (inp1 < 1))
{
double z = sqrt(-log((1-inp1)/2));
return ((((c[3]*z+c[2]) * z+c[1]) * z+c[0]) / ((d[1]*z+d[0]) * z+1)); //Inverse error formula
}
else if ((inp1 > -1) && (inp1 < 0.7))
{
double z = sqrt(-log((1+inp1)/2));
return (-(((c[3]*z+c[2]) * z+c[1]) * z+c[0]) / ((d[1]*z+d[0]) * z+1)); //Inverse error formula
}
}
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