Squashed 'third_party/boostorg/odeint/' content from commit 6ff2719
Change-Id: If4892e29c1a5e6cf3a7aa51486a2725c251b0c7d
git-subtree-dir: third_party/boostorg/odeint
git-subtree-split: 6ff2719b6907b86596c3d43e88c1bcfdf29df560
diff --git a/examples/multiprecision/cmp_precision.cpp b/examples/multiprecision/cmp_precision.cpp
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+++ b/examples/multiprecision/cmp_precision.cpp
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+/* 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;
+ }
+}