Drake
ScalarInitialValueProblem< T > Class Template Reference

A thin wrapper of the InitialValueProblem class to provide a simple interface when solving scalar initial value problems i.e. More...

#include <drake/systems/analysis/scalar_initial_value_problem.h>

Classes

struct  SpecifiedValues
 A collection of values i.e. More...
 

Public Types

typedef std::function< T(const T &t, const T &x, const VectorX< T > &k)> ScalarODEFunction
 Scalar ODE dx/dt = f(t, x; ๐ค) function type. More...
 

Public Member Functions

 ScalarInitialValueProblem (const ScalarODEFunction &scalar_ode_function, const SpecifiedValues &default_values)
 Constructs an scalar IVP described by the given scalar_ode_function, using given default_values.t0 and default_values.x0 as initial conditions, and parameterized with default_values.k by default. More...
 
Solve (const T &tf, const SpecifiedValues &values={}) const
 Solves the IVP for time tf, using the initial time tโ‚€, initial state xโ‚€ and parameter vector ๐ค present in values, falling back to the ones given on construction if not given. More...
 
template<typename Integrator , typename... Args>
Integratorreset_integrator (Args &&...args)
 Resets the internal integrator instance by in-place construction of the given integrator type. More...
 
const IntegratorBase< T > * get_integrator () const
 Gets a pointer to the internal integrator instance. More...
 
IntegratorBase< T > * get_mutable_integrator ()
 Gets a pointer to the internal mutable integrator instance. More...
 
Does not allow copy, move, or assignment
 ScalarInitialValueProblem (const ScalarInitialValueProblem &)=delete
 
ScalarInitialValueProblemoperator= (const ScalarInitialValueProblem &)=delete
 
 ScalarInitialValueProblem (ScalarInitialValueProblem &&)=delete
 
ScalarInitialValueProblemoperator= (ScalarInitialValueProblem &&)=delete
 

Detailed Description

template<typename T>
class drake::systems::ScalarInitialValueProblem< T >

A thin wrapper of the InitialValueProblem class to provide a simple interface when solving scalar initial value problems i.e.

when evaluating the x(t; ๐ค) solution function to the given ODE dx/dt = f(t, x; ๐ค), where f : t โจฏ x โ†’ โ„ , t โˆˆ โ„, x โˆˆ โ„, ๐ค โˆˆ โ„แต, along with an initial condition x(tโ‚€; ๐ค) = xโ‚€. The parameter vector ๐ค allows for generic IVP definitions, which can later be solved for any instance of said vector.

Note the distinction from general initial value problems where f : t โจฏ ๐ฑ โ†’ โ„โฟ and ๐ฑ โˆˆ โ„โฟ, addressed by the class being wrapped. While every scalar initial value problem could be written in vector form, this wrapper keeps both problem definition and solution in their scalar form with almost zero overhead, leading to clearer code if applicable. Moreover, this scalar form facilitates single-dimensional quadrature using methods for solving initial value problems.

For further insight into its use, consider the following examples of scalar IVPs:

  • The population growth of an hypothetical bacteria colony is described by dN/dt = r * N. The colony has Nโ‚€ subjects at time tโ‚€. In this context, x โ‰œ N, xโ‚€ โ‰œ Nโ‚€, ๐ค โ‰œ [r], dx/dt = f(t, x; ๐ค) = ๐คโ‚ * x.
  • The charge Q stored in the capacitor of a (potentially equivalent) series RC circuit driven by a time varying voltage source E(t) can be described by dQ/dt = (E(t) - Q / Cs) / Rs, where Rs refers to the resistor's resistance and Cs refers to the capacitor's capacitance. In this context, and assuming an initial stored charge Qโ‚€ at time tโ‚€, x โ‰œ Q, ๐ค โ‰œ [Rs, Cs], xโ‚€ โ‰œ Qโ‚€, dx/dt = f(t, x; ๐ค) = (E(t) - x / ๐คโ‚‚) / ๐คโ‚.
Template Parameters
TThe โ„ domain scalar type, which must be a valid Eigen scalar.
Note
Instantiated templates for the following scalar types T are provided:
  • double

Member Typedef Documentation

typedef std::function<T(const T& t, const T& x, const VectorX<T>& k)> ScalarODEFunction

Scalar ODE dx/dt = f(t, x; ๐ค) function type.

Parameters
tThe independent variable t โˆˆ โ„ .
xThe dependent variable x โˆˆ โ„ .
kThe parameter vector ๐ค โˆˆ โ„แต.
Returns
The derivative dx/dt โˆˆ โ„.

Constructor & Destructor Documentation

ScalarInitialValueProblem ( const ScalarODEFunction scalar_ode_function,
const SpecifiedValues default_values 
)
inline

Constructs an scalar IVP described by the given scalar_ode_function, using given default_values.t0 and default_values.x0 as initial conditions, and parameterized with default_values.k by default.

Parameters
scalar_ode_functionThe ODE function f(t, x; ๐ค) that describes the state evolution over time.
default_valuesThe values specified by default for this IVP, i.e. default initial time tโ‚€ โˆˆ โ„ and state xโ‚€ โˆˆ โ„, and default parameter vector ๐ค โˆˆ โ„แต.
Precondition
An initial time default_values.t0 is provided.
An initial state default_values.x0 is provided.
An parameter vector default_values.k is provided.
Exceptions
std::logic_errorif preconditions are not met.

Member Function Documentation

const IntegratorBase<T>* get_integrator ( ) const
inline

Gets a pointer to the internal integrator instance.

IntegratorBase<T>* get_mutable_integrator ( )
inline

Gets a pointer to the internal mutable integrator instance.

ScalarInitialValueProblem& operator= ( ScalarInitialValueProblem< T > &&  )
delete
ScalarInitialValueProblem& operator= ( const ScalarInitialValueProblem< T > &  )
delete
Integrator* reset_integrator ( Args &&...  args)
inline

Resets the internal integrator instance by in-place construction of the given integrator type.

A usage example is shown below.

scalar_ivp.reset_integrator<RungeKutta2Integrator<T>>(max_step);
Parameters
argsThe integrator type-specific arguments.
Returns
The new integrator instance.
Template Parameters
IntegratorThe integrator type, which must be an IntegratorBase subclass.
ArgsThe integrator specific argument types.
Warning
This operation invalidates pointers returned by ScalarInitialValueProblem::get_integrator() and ScalarInitialValueProblem::get_mutable_integrator().
T Solve ( const T &  tf,
const SpecifiedValues values = {} 
) const
inline

Solves the IVP for time tf, using the initial time tโ‚€, initial state xโ‚€ and parameter vector ๐ค present in values, falling back to the ones given on construction if not given.

Parameters
tfThe time to solve the IVP for.
valuesThe specified values for the IVP.
Returns
The IVP solution x(tf; ๐ค) for x(tโ‚€; ๐ค) = xโ‚€.
Precondition
Given tf must be larger than or equal to the specified initial time tโ‚€ (either given or default).
If given, the dimension of the parameter vector values.k must match that of the parameter vector in the default specified values given on construction.
Exceptions
std::logic_errorif preconditions are not met.

The documentation for this class was generated from the following file: