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// $Id: parsed_function.h 20602 2010-02-13 17:44:17Z bangerth $
// Version: $Name$
//
// Copyright (C) 2007, 2009 by the deal.II authors
//
// This file is subject to QPL and may not be distributed
// without copyright and license information. Please refer
// to the file deal.II/doc/license.html for the text and
// further information on this license.
//
//---------------------------------------------------------------------------
#ifndef __deal2__parsed_function_h
#define __deal2__parsed_function_h
#include <base/auto_derivative_function.h>
#include <base/function_parser.h>
#include <base/parameter_handler.h>
DEAL_II_NAMESPACE_OPEN
namespace Functions
{
/**
* Friendly interface to the FunctionParser class. This class is
* meant as a wrapper for the FunctionParser class. It is used in the
* step-34 tutorial program.
*
* It provides two
* methods to declare and parse a ParameterHandler object and creates
* the Function object declared in the parameter file. This class is
* derived from the AutoDerivativeFunction class, so you don't need
* to specify derivatives. An example of usage of this class is as follows:
*
* @code
* // A parameter handler
* ParameterHandler prm;
*
* // Declare a section for the function we need
* prm.enter_subsection("My vector function");
* ParsedFunction<dim>::declare_parameters(prm, dim);
* prm.leave_subsection();
*
* // Create a ParsedFunction
* ParsedFunction<dim> my_vector_function(dim);
*
* // Parse an input file.
* prm.read_input(some_input_file);
*
* // Initialize the ParsedFunction object with the given file
* prm.enter_subsection("My vector function");
* my_vector_function.parse_parameters(prm);
* prm.leave_subsection();
*
* @endcode
*
* And here is an example of how the input parameter could look like
* (see the documentation of the FunctionParser class for a detailed
* description of the syntax of the function definition):
*
* @code
*
* # A test two dimensional vector function, depending on time
* subsection My vector function
* set Function constants = kappa=.1, lambda=2.
* set Function expression = if(y>.5, kappa*x*(1-x),0); t^2*cos(lambda*pi*x)
* set Variable names = x,y,t
* end
*
* @endcode
*
* @ingroup functions
* @author Luca Heltai, 2006
*/
template <int dim>
class ParsedFunction : public AutoDerivativeFunction<dim>
{
public:
/**
* Construct a vector
* function. The vector
* function which is generated
* has @p n_components
* components (defaults to
* 1). The parameter @p h is
* used to initialize the
* AutoDerivativeFunction class
* from which this class is
* derived.
*/
ParsedFunction (const unsigned int n_components = 1, const double h=1e-8);
/**
* Declare parameters needed by
* this class. The additional
* parameter @p n_components is
* used to generate the right
* code according to the number
* of components of the
* function that will parse
* this ParameterHandler. If
* the number of components
* which is parsed does not
* match the number of
* components of this object,
* an assertion is thrown and
* the program is aborted. The
* default behavior for this
* class is to declare the
* following entries:
*
* @code
*
* set Function constants =
* set Function expression = 0
* set Variable names = x,y,t
*
* @endcode
*
*/
static void declare_parameters(ParameterHandler &prm,
const unsigned int n_components = 1);
/**
* Parse parameters needed by
* this class. If the number
* of components which is
* parsed does not match the
* number of components of this
* object, an assertion is
* thrown and the program is
* aborted. In order for the
* class to function properly,
* we follow the same
* convenctions declared in the
* FunctionParser class (look
* there for a detailed
* description of the syntax
* for function declarations).
*
* The three variables that can
* be parsed from a parameter
* file are the following:
*
* @code
*
* set Function constants =
* set Function expression =
* set Variable names =
*
* @endcode
*
* Function constants is a
* collection of pairs in the
* form name=value, separated
* by commas, for example:
*
* @code
*
* set Function constants = lambda=1. , alpha=2., gamma=3.
*
* @endcode
*
* These constants can be used
* in the declaration of the
* function expression, which
* follows the convention of
* the FunctionParser
* class. In order to specify
* vector functions,
* semicolons have to be used
* to separate the different
* components, e.g.:
*
* @code
*
* set Function expression = cos(pi*x) ; cos(pi*y)
*
* @endcode
*
* The variable names entry
* can be used to customize
* the name of the variables
* used in the Function. It
* defaults to
*
* @code
*
* set Variable names = x,t
*
* @endcode
*
* for one dimensional problems,
*
* @code
*
* set Variable names = x,y,t
*
* @endcode
*
* for two dimensional problems and
*
* @code
*
* set Variable names = x,y,z,t
*
* @endcode
*
* for three dimensional problems.
*
* The time variable can be
* set according to
* specifications in the
* FunctionTime base class.
*/
void parse_parameters(ParameterHandler &prm);
/**
* Get one value at the given
* point.
*/
virtual void vector_value (const Point<dim> &p,
Vector<double> &values) const;
/**
* Return the value of the
* function at the given
* point. Unless there is only
* one component (i.e. the
* function is scalar), you
* should state the component
* you want to have evaluated;
* it defaults to zero,
* i.e. the first component.
*/
virtual double value (const Point< dim > & p,
const unsigned int component = 0) const;
/**
* Set the time to a specific
* value for time-dependent
* functions.
*
* We need to overwrite this to
* set the time also in the
* accessor
* FunctionParser<dim>.
*/
virtual void set_time(const double newtime);
private:
/**
* The object with which we do
* computations.
*/
FunctionParser<dim> function_object;
};
}
DEAL_II_NAMESPACE_CLOSE
#endif
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