Fehlberg¶
(Source code, png, hires.png, pdf)

class
Fehlberg
(*args)¶ Adaptive order Fehlberg method.
 Parameters
 transitionFunction
Function
The function defining the flow of the ordinary differential equation. Must have one parameter.
 localPrecisionfloat
The expected absolute error on one step.
 orderint,
The order of the method, ie the exponent in the estimate of the local error for a step of size written as .
 transitionFunction
See also
Notes
The Fehlberg method of order is a onestep explicit method made of two embedded Runge Kutta methods of order and . More precisely, such a method approximate the solution of:
at a given set of locations by first building an approximation over an adapted grid with a number of points not necessarily equal to the number of locations and internal nodes not necessarily part of the set of locations. Then, the solution is approximated by a smooth piecewise polynomial function using
PiecewiseHermiteEvaluation
, which is evaluated over the set of locations.The method proceeds as follows. Knowing the solution at location and a current time step , two approximations and of are built, such that:
where we assume that:
The evolution operators and are constructed as follows:
with . The most desirable property of these methods is their embedded nature: the highorder approximation reuses all the evaluations of needed by the loworder approximation. The coefficients , , and fully specify the method.
For we have:
0
0
0
1
1/2
1
1
1
1/2
For we have:
0
0
0
1/256
1/512
1
1/2
1/2
255/256
255/256
2
1
1/256
255/256
1/512
For we have:
0
0
0
214/891
533/2106
1
1/4
1/4
1/33
0
2
27/40
189/800
214/891
650/891
800/1053
3
1
729/800
1/35
650/891
1/78
For the coefficients can be found eg in the C++ source code. For additional theory on these methods see [stoer1993], chapter 7.
Examples
>>> import openturns as ot >>> f = ot.SymbolicFunction(['t', 'y0', 'y1'], ['t  y0', 'y1 + t^2']) >>> phi = ot.ParametricFunction(f, [0], [0.0]) >>> solver = ot.Fehlberg(phi) >>> Y0 = [1.0, 1.0] >>> nt = 100 >>> timeGrid = [(i**2.0) / (nt  1.0)**2.0 for i in range(nt)] >>> result = solver.solve(Y0, timeGrid)
Methods
Accessor to the object’s name.
getId
()Accessor to the object’s id.
getName
()Accessor to the object’s name.
Accessor to the object’s shadowed id.
Transition function accessor.
Accessor to the object’s visibility state.
hasName
()Test if the object is named.
Test if the object has a distinguishable name.
setName
(name)Accessor to the object’s name.
setShadowedId
(id)Accessor to the object’s shadowed id.
setTransitionFunction
(transitionFunction)Transition function accessor.
setVisibility
(visible)Accessor to the object’s visibility state.
solve
(*args)Solve ODE.

__init__
(*args)¶ Initialize self. See help(type(self)) for accurate signature.

getClassName
()¶ Accessor to the object’s name.
 Returns
 class_namestr
The object class name (object.__class__.__name__).

getId
()¶ Accessor to the object’s id.
 Returns
 idint
Internal unique identifier.

getName
()¶ Accessor to the object’s name.
 Returns
 namestr
The name of the object.

getShadowedId
()¶ Accessor to the object’s shadowed id.
 Returns
 idint
Internal unique identifier.

getTransitionFunction
()¶ Transition function accessor.
 Returns
 transitionFunction
FieldFunction
Transition function.
 transitionFunction

getVisibility
()¶ Accessor to the object’s visibility state.
 Returns
 visiblebool
Visibility flag.

hasName
()¶ Test if the object is named.
 Returns
 hasNamebool
True if the name is not empty.

hasVisibleName
()¶ Test if the object has a distinguishable name.
 Returns
 hasVisibleNamebool
True if the name is not empty and not the default one.

setName
(name)¶ Accessor to the object’s name.
 Parameters
 namestr
The name of the object.

setShadowedId
(id)¶ Accessor to the object’s shadowed id.
 Parameters
 idint
Internal unique identifier.

setTransitionFunction
(transitionFunction)¶ Transition function accessor.
 Parameters
 transitionFunction
FieldFunction
Transition function.
 transitionFunction

setVisibility
(visible)¶ Accessor to the object’s visibility state.
 Parameters
 visiblebool
Visibility flag.