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82 lines
2.2 KiB
Plaintext
82 lines
2.2 KiB
Plaintext
/*
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Copyright 2011-2012 Karsten Ahnert
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Copyright 2013 Mario Mulansky
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE_1_0.txt or
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copy at http://www.boost.org/LICENSE_1_0.txt)
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*/
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/*
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* Solves many relaxation equations dxdt = - a * x in parallel and for different values of a.
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* The relaxation equations are completely uncoupled.
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*/
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#include <thrust/device_vector.h>
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#include <boost/ref.hpp>
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#include <boost/numeric/odeint.hpp>
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#include <boost/numeric/odeint/external/thrust/thrust.hpp>
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using namespace std;
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using namespace boost::numeric::odeint;
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// change to float if your GPU does not support doubles
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typedef double value_type;
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typedef thrust::device_vector< value_type > state_type;
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typedef runge_kutta4< state_type , value_type , state_type , value_type > stepper_type;
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struct relaxation
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{
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struct relaxation_functor
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{
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template< class T >
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__host__ __device__
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void operator()( T t ) const
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{
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// unpack the parameter we want to vary and the Lorenz variables
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value_type a = thrust::get< 1 >( t );
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value_type x = thrust::get< 0 >( t );
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thrust::get< 2 >( t ) = -a * x;
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}
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};
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relaxation( size_t N , const state_type &a )
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: m_N( N ) , m_a( a ) { }
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void operator()( const state_type &x , state_type &dxdt , value_type t ) const
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{
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thrust::for_each(
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thrust::make_zip_iterator( thrust::make_tuple( x.begin() , m_a.begin() , dxdt.begin() ) ) ,
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thrust::make_zip_iterator( thrust::make_tuple( x.end() , m_a.end() , dxdt.end() ) ) ,
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relaxation_functor() );
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}
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size_t m_N;
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const state_type &m_a;
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};
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const size_t N = 1024 * 1024;
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const value_type dt = 0.01;
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int main( int arc , char* argv[] )
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{
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// initialize the relaxation constants a
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vector< value_type > a_host( N );
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for( size_t i=0 ; i<N ; ++i ) a_host[i] = drand48();
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state_type a = a_host;
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// initialize the intial state x
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state_type x( N );
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thrust::fill( x.begin() , x.end() , 1.0 );
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// integrate
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relaxation relax( N , a );
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integrate_const( stepper_type() , boost::ref( relax ) , x , 0.0 , 10.0 , dt );
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return 0;
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}
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