Reference documentation for deal.II version Git 035d1ad 20180817 19:42:27 0400

#include <deal.II/base/function_time.h>
Public Member Functions  
FunctionTime (const Number initial_time=Number(0.0))  
virtual  ~FunctionTime ()=default 
Number  get_time () const 
virtual void  set_time (const Number new_time) 
virtual void  advance_time (const Number delta_t) 
Private Attributes  
Number  time 
Support for time dependent functions. The library was also designed for time dependent problems. For this purpose, the function objects also contain a field which stores the time, as well as functions manipulating them. Time independent problems should not access or even abuse them for other purposes, but since one normally does not create thousands of function objects, the gain in generality weighs out the fact that we need not store the time value for not time dependent problems. The second advantage is that the derived standard classes like ZeroFunction
, ConstantFunction
etc also work for time dependent problems.
Access to the time goes through the following functions:
* <li> <tt>get_time</tt>: return the present value of the time variable. * <li> <tt>set_time</tt>: set the time value to a specific value. * <li> <tt>advance_time</tt>: increase the time by a certain time step. *
The latter two functions are virtual, so that derived classes can perform computations which need only be done once for every new time. For example, if a time dependent function had a factor sin(t)
, then it may be a reasonable choice to calculate this factor in a derived version of set_time(), store it in a member variable and use that one rather than computing it every time value()
, value_list
or one of the other functions of class Function is called.
By default, the advance_time() function calls the set_time() function with the new time, so it is sufficient in most cases to overload only set_time() for computations as sketched out above.
The constructor of this class takes an initial value for the time variable, which defaults to zero. Because a default value is given, none of the derived classes needs to take an initial value for the time variable if not needed.
Number  The data type in which time values are to be stored. This will, in almost all cases, simply be the default double , but there are cases where one may want to store the time in a different (and always scalar) type. An example would be an interval type that can store a value as well as its uncertainty. Another example would be a type that allows for Automatic Differentiation (see, for example, the Sacado type used in step33) and thereby can generate analytic (temporal) derivatives of a function. 
Definition at line 73 of file function_time.h.
FunctionTime< Number >::FunctionTime  (  const Number  initial_time = Number(0.0)  ) 
Constructor. May take an initial value for the time variable, which defaults to zero.

virtualdefault 
Virtual destructor.
Number FunctionTime< Number >::get_time  (  )  const 
Return the value of the time variable.

virtual 
Set the time to new_time
, overwriting the old value.

virtual 
Advance the time by the given time step delta_t
.

private 
Store the present time.
Definition at line 109 of file function_time.h.