mirror of
https://github.com/saitohirga/WSJT-X.git
synced 2025-10-31 04:50:34 -04:00
69 lines
1.9 KiB
C++
69 lines
1.9 KiB
C++
/* Boost libs/numeric/odeint/examples/multiprecision/cmp_precision.cpp
|
|
|
|
Copyright 2013 Karsten Ahnert
|
|
Copyright 2013 Mario Mulansky
|
|
|
|
example comparing double to multiprecision using Boost.Multiprecision
|
|
|
|
Distributed under the Boost Software License, Version 1.0.
|
|
(See accompanying file LICENSE_1_0.txt or
|
|
copy at http://www.boost.org/LICENSE_1_0.txt)
|
|
*/
|
|
|
|
|
|
#include <iostream>
|
|
#include <boost/numeric/odeint.hpp>
|
|
#include <boost/multiprecision/cpp_dec_float.hpp>
|
|
|
|
using namespace std;
|
|
using namespace boost::numeric::odeint;
|
|
|
|
typedef boost::multiprecision::cpp_dec_float_50 mp_50;
|
|
|
|
/* we solve the simple ODE x' = 3/(2t^2) + x/(2t)
|
|
* with initial condition x(1) = 0.
|
|
* Analytic solution is x(t) = sqrt(t) - 1/t
|
|
*/
|
|
|
|
void rhs_m( const mp_50 x , mp_50 &dxdt , const mp_50 t )
|
|
{ // version for multiprecision
|
|
dxdt = mp_50(3)/(mp_50(2)*t*t) + x/(mp_50(2)*t);
|
|
}
|
|
|
|
void rhs_d( const double x , double &dxdt , const double t )
|
|
{ // version for double precision
|
|
dxdt = 3.0/(2.0*t*t) + x/(2.0*t);
|
|
}
|
|
|
|
// state_type = mp_50 = deriv_type = time_type = mp_50
|
|
typedef runge_kutta4< mp_50 , mp_50 , mp_50 , mp_50 , vector_space_algebra , default_operations , never_resizer > stepper_type_m;
|
|
|
|
typedef runge_kutta4< double , double , double , double , vector_space_algebra , default_operations , never_resizer > stepper_type_d;
|
|
|
|
int main()
|
|
{
|
|
|
|
stepper_type_m stepper_m;
|
|
stepper_type_d stepper_d;
|
|
|
|
mp_50 dt_m( 0.5 );
|
|
double dt_d( 0.5 );
|
|
|
|
cout << "dt" << '\t' << "mp" << '\t' << "double" << endl;
|
|
|
|
while( dt_m > 1E-20 )
|
|
{
|
|
|
|
mp_50 x_m = 0; //initial value x(1) = 0
|
|
stepper_m.do_step( rhs_m , x_m , mp_50( 1 ) , dt_m );
|
|
double x_d = 0;
|
|
stepper_d.do_step( rhs_d , x_d , 1.0 , dt_d );
|
|
|
|
cout << dt_m << '\t';
|
|
cout << abs((x_m - (sqrt(1+dt_m)-mp_50(1)/(1+dt_m)))/x_m) << '\t' ;
|
|
cout << abs((x_d - (sqrt(1+dt_d)-mp_50(1)/(1+dt_d)))/x_d) << endl ;
|
|
dt_m /= 2;
|
|
dt_d /= 2;
|
|
}
|
|
}
|