Functions::ParsedFunction< dim > Class Template Reference
[Functions]

Inheritance diagram for Functions::ParsedFunction< dim >:

Inheritance graph
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List of all members.

Public Member Functions

 ParsedFunction (const unsigned int n_components=1, const double h=1e-8)
void parse_parameters (ParameterHandler &prm)
virtual void vector_value (const Point< dim > &p, Vector< double > &values) const
virtual double value (const Point< dim > &p, const unsigned int component=0) const
virtual void set_time (const double newtime)

Static Public Member Functions

static void declare_parameters (ParameterHandler &prm, const unsigned int n_components=1)

Private Attributes

FunctionParser< dim > function_object


Detailed Description

template<int dim>
class Functions::ParsedFunction< dim >

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:

   // 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();

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):

   # 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

Author:
Luca Heltai, 2006

Constructor & Destructor Documentation

template<int dim>
Functions::ParsedFunction< dim >::ParsedFunction ( const unsigned int  n_components = 1,
const double  h = 1e-8 
)

Construct a vector function. The vector function which is generated has n_components components (defaults to 1). The parameter h is used to initialize the AutoDerivativeFunction class from which this class is derived.


Member Function Documentation

template<int dim>
static void Functions::ParsedFunction< dim >::declare_parameters ( ParameterHandler prm,
const unsigned int  n_components = 1 
) [static]

Declare parameters needed by this class. The additional parameter 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:

  set Function constants  = 
  set Function expression = 0
  set Variable names      = x,y,t

template<int dim>
void Functions::ParsedFunction< dim >::parse_parameters ( ParameterHandler prm  ) 

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:

  set Function constants  = 
  set Function expression = 
  set Variable names      = 

Function constants is a collection of pairs in the form name=value, separated by commas, for example:

  set Function constants = lambda=1. , alpha=2., gamma=3.

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.:

  set Function expression = cos(pi*x) ; cos(pi*y) 

The variable names entry can be used to customize the name of the variables used in the Function. It defaults to

  set Variable names      = x,t

for one dimensional problems,

  set Variable names      = x,y,t

for two dimensional problems and

  set Variable names      = x,y,z,t

for three dimensional problems.

The time variable can be set according to specifications in the FunctionTime base class.

template<int dim>
virtual void Functions::ParsedFunction< dim >::vector_value ( const Point< dim > &  p,
Vector< double > &  values 
) const [virtual]

Get one value at the given point.

Reimplemented from Function< dim >.

template<int dim>
virtual double Functions::ParsedFunction< dim >::value ( const Point< dim > &  p,
const unsigned int  component = 0 
) const [virtual]

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.

Reimplemented from Function< dim >.

template<int dim>
virtual void Functions::ParsedFunction< dim >::set_time ( const double  newtime  )  [virtual]

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>.

Reimplemented from FunctionTime.


Member Data Documentation

template<int dim>
FunctionParser<dim> Functions::ParsedFunction< dim >::function_object [private]

The object with which we do computations.


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

deal.II documentation generated on Sat Aug 15 16:52:34 2009 by doxygen 1.5.9