functors.h

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#pragma once
#include <boost/math/special_functions.hpp>
namespace dg {
namespace mat {
template < class T = double>
struct BESSELI0
{
    BESSELI0( ) {}
    T operator() ( T x) const
    {
        return boost::math::cyl_bessel_i(0, x);
    }
};
template < class T = double>
struct GAMMA0
{
    GAMMA0( ) {}
    T operator() ( T x) const
    {
        return exp(x)*boost::math::cyl_bessel_i(0, x);
    }
};
 
 
template<class T>
T phi1( T x){
    if ( fabs( x) < 1e-16 )
        return 1.;
    if ( fabs(x) < 1)
        return expm1( x)/x;
    return (exp( x) - 1)/x;
}
 
template<class T>
T phi2( T x){
    if ( fabs( x) < 1e-16 )
        return 1./2;
    if ( fabs(x) < 1e-2)
        return 1./2.+x*(1./6.+x*(1./24. + x/120.));
    return ((exp( x) - 1)/x - 1)/x;
}
 
template<class T>
T phi3( T x){
    if ( fabs( x) < 1e-16 )
        return 1./6.;
    if ( fabs(x) < 1e-2)
        return 1./6. + x*(1./24.+x*(1./120. +x/720.));
    return (((exp( x) - 1)/x - 1)/x-1./2.)/x;
}
template<class T>
T phi4( T x){
    if ( fabs( x) < 1e-16 )
        return 1./24.;
    if ( fabs(x) < 1e-2)
        return 1./24. + x*(1./120.+x*(1./720. + x/5040));
    return ((((exp( x) - 1)/x - 1)/x-1./2.)/x-1./6.)/x;
}
 
}//namespace mat
}//namespace dg