3 boost/numeric/odeint/stepper/base/explicit_stepper_base.hpp
6 Base class for all explicit Runge Kutta steppers.
9 Copyright 2010-2013 Karsten Ahnert
10 Copyright 2010-2012 Mario Mulansky
11 Copyright 2012 Christoph Koke
13 Distributed under the Boost Software License, Version 1.0.
14 (See accompanying file LICENSE_1_0.txt or
15 copy at http://www.boost.org/LICENSE_1_0.txt)
19 #ifndef BOOST_NUMERIC_ODEINT_STEPPER_BASE_EXPLICIT_STEPPER_BASE_HPP_INCLUDED
20 #define BOOST_NUMERIC_ODEINT_STEPPER_BASE_EXPLICIT_STEPPER_BASE_HPP_INCLUDED
23 #include <boost/utility/enable_if.hpp>
24 #include <boost/type_traits/is_same.hpp>
26 #include <boost/numeric/odeint/util/bind.hpp>
27 #include <boost/numeric/odeint/util/unwrap_reference.hpp>
29 #include <boost/numeric/odeint/util/state_wrapper.hpp>
30 #include <boost/numeric/odeint/util/resizer.hpp>
31 #include <boost/numeric/odeint/util/is_resizeable.hpp>
33 #include <boost/numeric/odeint/stepper/stepper_categories.hpp>
35 #include <boost/numeric/odeint/stepper/base/algebra_stepper_base.hpp>
42 * base class for explicit steppers
43 * models the stepper concept
45 * this class provides the following overloads
46 * do_step( sys , x , t , dt )
47 * do_step( sys , in , t , out , dt )
48 * do_step( sys , x , dxdt_in , t , dt )
49 * do_step( sys , in , dxdt_in , t , out , dt )
54 unsigned short Order ,
63 class explicit_stepper_base : public algebra_stepper_base< Algebra , Operations >
68 typedef explicit_stepper_base< Stepper , Order , State , Value , Deriv , Time , Algebra , Operations , Resizer > internal_stepper_base_type;
69 #endif // DOXYGEN_SKIP
72 typedef State state_type;
73 typedef Value value_type;
74 typedef Deriv deriv_type;
75 typedef Time time_type;
76 typedef Resizer resizer_type;
77 typedef Stepper stepper_type;
78 typedef stepper_tag stepper_category;
79 typedef algebra_stepper_base< Algebra , Operations > algebra_stepper_base_type;
80 typedef typename algebra_stepper_base_type::algebra_type algebra_type;
81 typedef typename algebra_stepper_base_type::operations_type operations_type;
82 typedef unsigned short order_type;
85 typedef state_wrapper< state_type > wrapped_state_type;
86 typedef state_wrapper< deriv_type > wrapped_deriv_type;
87 #endif // DOXYGEN_SKIP
90 static const order_type order_value = Order;
93 explicit_stepper_base( const algebra_type &algebra = algebra_type() )
94 : algebra_stepper_base_type( algebra )
98 * \return Returns the order of the stepper.
100 order_type order( void ) const
107 * Version 1 : do_step( sys , x , t , dt )
109 * the two overloads are needed in order to solve the forwarding problem
111 template< class System , class StateInOut >
112 void do_step( System system , StateInOut &x , time_type t , time_type dt )
114 do_step_v1( system , x , t , dt );
118 * \brief Second version to solve the forwarding problem, can be called with Boost.Range as StateInOut.
120 template< class System , class StateInOut >
121 void do_step( System system , const StateInOut &x , time_type t , time_type dt )
123 do_step_v1( system , x , t , dt );
127 * Version 2 : do_step( sys , x , dxdt , t , dt )
129 * this version does not solve the forwarding problem, boost.range can not be used
131 * the disable is needed to avoid ambiguous overloads if state_type = time_type
133 template< class System , class StateInOut , class DerivIn >
134 typename boost::disable_if< boost::is_same< DerivIn , time_type > , void >::type
135 do_step( System system , StateInOut &x , const DerivIn &dxdt , time_type t , time_type dt )
137 this->stepper().do_step_impl( system , x , dxdt , t , x , dt );
142 * named Version 2: do_step_dxdt_impl( sys , in , dxdt , t , dt )
144 * this version is needed when this stepper is used for initializing
145 * multistep stepper like adams-bashforth. Hence we provide an explicitely
146 * named version that is not disabled. Meant for internal use only.
148 template < class System, class StateInOut, class DerivIn >
149 void do_step_dxdt_impl( System system, StateInOut &x, const DerivIn &dxdt,
150 time_type t, time_type dt )
152 this->stepper().do_step_impl( system , x , dxdt , t , x , dt );
157 * Version 3 : do_step( sys , in , t , out , dt )
159 * this version does not solve the forwarding problem, boost.range can not be used
161 template< class System , class StateIn , class StateOut >
162 void do_step( System system , const StateIn &in , time_type t , StateOut &out , time_type dt )
164 typename odeint::unwrap_reference< System >::type &sys = system;
165 m_resizer.adjust_size( in , detail::bind( &internal_stepper_base_type::template resize_impl<StateIn> , detail::ref( *this ) , detail::_1 ) );
166 sys( in , m_dxdt.m_v ,t );
167 this->stepper().do_step_impl( system , in , m_dxdt.m_v , t , out , dt );
172 * Version 4 : do_step( sys , in , dxdt , t , out , dt )
174 * this version does not solve the forwarding problem, boost.range can not be used
176 template< class System , class StateIn , class DerivIn , class StateOut >
177 void do_step( System system , const StateIn &in , const DerivIn &dxdt , time_type t , StateOut &out , time_type dt )
179 this->stepper().do_step_impl( system , in , dxdt , t , out , dt );
184 * named Version 4: do_step_dxdt_impl( sys , in , dxdt , t , out, dt )
186 * this version is needed when this stepper is used for initializing
187 * multistep stepper like adams-bashforth. Hence we provide an explicitely
188 * named version. Meant for internal use only.
190 template < class System, class StateIn, class DerivIn, class StateOut >
191 void do_step_dxdt_impl( System system, const StateIn &in,
192 const DerivIn &dxdt, time_type t, StateOut &out,
195 this->stepper().do_step_impl( system , in , dxdt , t , out , dt );
198 template< class StateIn >
199 void adjust_size( const StateIn &x )
206 stepper_type& stepper( void )
208 return *static_cast< stepper_type* >( this );
211 const stepper_type& stepper( void ) const
213 return *static_cast< const stepper_type* >( this );
217 template< class StateIn >
218 bool resize_impl( const StateIn &x )
220 return adjust_size_by_resizeability( m_dxdt , x , typename is_resizeable<deriv_type>::type() );
224 template< class System , class StateInOut >
225 void do_step_v1( System system , StateInOut &x , time_type t , time_type dt )
227 typename odeint::unwrap_reference< System >::type &sys = system;
228 m_resizer.adjust_size( x , detail::bind( &internal_stepper_base_type::template resize_impl< StateInOut > , detail::ref( *this ) , detail::_1 ) );
229 sys( x , m_dxdt.m_v ,t );
230 this->stepper().do_step_impl( system , x , m_dxdt.m_v , t , x , dt );
234 resizer_type m_resizer;
238 wrapped_deriv_type m_dxdt;
242 /******* DOXYGEN *********/
245 * \class explicit_stepper_base
246 * \brief Base class for explicit steppers without step size control and without dense output.
248 * This class serves as the base class for all explicit steppers with algebra and operations.
249 * Step size control and error estimation as well as dense output are not provided. explicit_stepper_base
250 * is used as the interface in a CRTP (currently recurring template pattern). In order to work
251 * correctly the parent class needs to have a method `do_step_impl( system , in , dxdt_in , t , out , dt )`.
252 * This is method is used by explicit_stepper_base. explicit_stepper_base derives from
253 * algebra_stepper_base. An example how this class can be used is
256 * template< class State , class Value , class Deriv , class Time , class Algebra , class Operations , class Resizer >
257 * class custom_euler : public explicit_stepper_base< 1 , State , Value , Deriv , Time , Algebra , Operations , Resizer >
261 * typedef explicit_stepper_base< 1 , State , Value , Deriv , Time , Algebra , Operations , Resizer > base_type;
263 * custom_euler( const Algebra &algebra = Algebra() ) { }
265 * template< class Sys , class StateIn , class DerivIn , class StateOut >
266 * void do_step_impl( Sys sys , const StateIn &in , const DerivIn &dxdt , Time t , StateOut &out , Time dt )
268 * m_algebra.for_each3( out , in , dxdt , Operations::scale_sum2< Value , Time >( 1.0 , dt );
271 * template< class State >
272 * void adjust_size( const State &x )
274 * base_type::adjust_size( x );
279 * For the Stepper concept only the `do_step( sys , x , t , dt )` needs to be implemented. But this class
280 * provides additional `do_step` variants since the stepper is explicit. These methods can be used to increase
281 * the performance in some situation, for example if one needs to analyze `dxdt` during each step. In this case
285 * sys( x , dxdt , t );
286 * stepper.do_step( sys , x , dxdt , t , dt ); // the value of dxdt is used here
290 * In detail explicit_stepper_base provides the following `do_step` variants
291 * - `do_step( sys , x , t , dt )` - The classical `do_step` method needed to fulfill the Stepper concept. The state is updated in-place.
292 * A type modelling a Boost.Range can be used for x.
293 * - `do_step( sys , in , t , out , dt )` - This method updates the state out-of-place, hence the result of the step is stored in `out`.
294 * - `do_step( sys , x , dxdt , t , dt )` - This method updates the state in-place, but the derivative at the point `t` must be
295 * explicitly passed in `dxdt`. For an example see the code snippet above.
296 * - `do_step( sys , in , dxdt , t , out , dt )` - This method update the state out-of-place and expects that the derivative at the point
297 * `t` is explicitly passed in `dxdt`. It is a combination of the two `do_step` methods above.
299 * \note The system is always passed as value, which might result in poor performance if it contains data. In this case it can be used with `boost::ref`
300 * or `std::ref`, for example `stepper.do_step( boost::ref( sys ) , x , t , dt );`
302 * \note The time `t` is not advanced by the stepper. This has to done manually, or by the appropriate `integrate` routines or `iterator`s.
304 * \tparam Stepper The stepper on which this class should work. It is used via CRTP, hence explicit_stepper_base
305 * provides the interface for the Stepper.
306 * \tparam Order The order of the stepper.
307 * \tparam State The state type for the stepper.
308 * \tparam Value The value type for the stepper. This should be a floating point type, like float,
309 * double, or a multiprecision type. It must not necessary be the value_type of the State. For example
310 * the State can be a `vector< complex< double > >` in this case the Value must be double.
311 * The default value is double.
312 * \tparam Deriv The type representing time derivatives of the state type. It is usually the same type as the
313 * state type, only if used with Boost.Units both types differ.
314 * \tparam Time The type representing the time. Usually the same type as the value type. When Boost.Units is
315 * used, this type has usually a unit.
316 * \tparam Algebra The algebra type which must fulfill the Algebra Concept.
317 * \tparam Operations The type for the operations which must fulfill the Operations Concept.
318 * \tparam Resizer The resizer policy class.
323 * \fn explicit_stepper_base::explicit_stepper_base( const algebra_type &algebra )
324 * \brief Constructs a explicit_stepper_base class. This constructor can be used as a default
325 * constructor if the algebra has a default constructor.
326 * \param algebra A copy of algebra is made and stored inside explicit_stepper_base.
330 * \fn explicit_stepper_base::order_type order( void ) const
331 * \return Returns the order of the stepper.
335 * \fn explicit_stepper_base::do_step( System system , StateInOut &x , time_type t , time_type dt )
336 * \brief This method performs one step. It transforms the result in-place.
338 * \param system The system function to solve, hence the r.h.s. of the ordinary differential equation. It must fulfill the
339 * Simple System concept.
340 * \param x The state of the ODE which should be solved. After calling do_step the result is updated in x.
341 * \param t The value of the time, at which the step should be performed.
342 * \param dt The step size.
347 * \fn explicit_stepper_base::do_step( System system , StateInOut &x , const DerivIn &dxdt , time_type t , time_type dt )
349 * \brief The method performs one step. Additionally to the other method
350 * the derivative of x is also passed to this method. It is supposed to be used in the following way:
353 * sys( x , dxdt , t );
354 * stepper.do_step( sys , x , dxdt , t , dt );
357 * The result is updated in place in x. This method is disabled if Time and Deriv are of the same type. In this
358 * case the method could not be distinguished from other `do_step` versions.
360 * \note This method does not solve the forwarding problem.
362 * \param system The system function to solve, hence the r.h.s. of the ODE. It must fulfill the
363 * Simple System concept.
364 * \param x The state of the ODE which should be solved. After calling do_step the result is updated in x.
365 * \param dxdt The derivative of x at t.
366 * \param t The value of the time, at which the step should be performed.
367 * \param dt The step size.
371 * \fn void explicit_stepper_base::do_step( System system , const StateIn &in , time_type t , StateOut &out , time_type dt )
372 * \brief The method performs one step. The state of the ODE is updated out-of-place.
373 * \note This method does not solve the forwarding problem.
375 * \param system The system function to solve, hence the r.h.s. of the ODE. It must fulfill the
376 * Simple System concept.
377 * \param in The state of the ODE which should be solved. in is not modified in this method
378 * \param t The value of the time, at which the step should be performed.
379 * \param out The result of the step is written in out.
380 * \param dt The step size.
384 * \fn void explicit_stepper_base::do_step( System system , const StateIn &in , const DerivIn &dxdt , time_type t , StateOut &out , time_type dt )
385 * \brief The method performs one step. The state of the ODE is updated out-of-place.
386 * Furthermore, the derivative of x at t is passed to the stepper.
387 * It is supposed to be used in the following way:
390 * sys( in , dxdt , t );
391 * stepper.do_step( sys , in , dxdt , t , out , dt );
394 * \note This method does not solve the forwarding problem.
396 * \param system The system function to solve, hence the r.h.s. of the ODE. It must fulfill the
397 * Simple System concept.
398 * \param in The state of the ODE which should be solved. in is not modified in this method
399 * \param dxdt The derivative of x at t.
400 * \param t The value of the time, at which the step should be performed.
401 * \param out The result of the step is written in out.
402 * \param dt The step size.
406 * \fn void explicit_stepper_base::adjust_size( const StateIn &x )
407 * \brief Adjust the size of all temporaries in the stepper manually.
408 * \param x A state from which the size of the temporaries to be resized is deduced.
415 #endif // BOOST_NUMERIC_ODEINT_STEPPER_BASE_EXPLICIT_STEPPER_BASE_HPP_INCLUDED