LOSDAR is a multistep method for solving explicit ordinary differential equations on the form,
\[\dot{y} = f(t,y), \quad y(t_0) = y_0.\]LSODAR automatically switches between using an ADAMS method or an BDF method and is also able to monitor events.
LSODAR is part of ODEPACK, http://www.netlib.org/odepack/opkd-sum
Import the solver together with the correct problem:
from assimulo.solvers import LSODAR
from assimulo.problem import Explicit_Problem
Define the problem, such as:
def rhs(t, y): #Note that y are a 1-D numpy array.
yd = -1.0
return N.array([yd]) #Note that the return must be numpy array, NOT a scalar.
y0 = [1.0]
t0 = 1.0
Create a problem instance:
mod = Explicit_Problem(rhs, y0, t0)
Note
For complex problems, it is recommended to check the available examples and the documentation in the problem class, Explicit_Problem
. It is also recommended to define your problem as a subclass of Explicit_Problem
.
Warning
When subclassing from a problem class, the function for calculating the right-hand-side (for ODEs) must be named rhs and in the case with a residual function (for DAEs) it must be named res.
Create a solver instance:
sim = LSODAR(mod)
Modify (optionally) the solver parameters.
Parameters:
atol
Defines the absolute tolerance(s) that is to be used by the solver.backward
Specifies if the simulation is done in reverse time.clock_step
Specifies if the elapsed time of an integrator step should be timed or not.display_progress
This option actives output during the integration in terms of that the current integration is periodically printed to the stdout.maxh
The absolute value of the maximal stepsize for all methods Parameters:: maxh - Default: 0.maxordn
The maximum order used by the Adams-Moulton method (nonstiff case) Parameters:: maxordn - Default 12 - Should be a positive integer.maxords
The maximum order used by the BDF method (stiff case) Parameters:: maxords - Default 5 - Should be a positive integer.maxsteps
The maximum number of steps allowed to be taken to reach the final time.num_threads
This options specifies the number of threads to be used for those solvers that supports it.report_continuously
This options specifies if the solver should report the solution continuously after steps.rkstarter
This defines how LSODAR is started.rtol
Defines the relative tolerance that is to be used by the solver.store_event_points
This options specifies if the solver should save additional points at the events, \(t_e^-, t_e^+\).time_limit
This option can be used to limit the time of an integration.usejac
This sets the option to use the user defined jacobian.verbosity
This determines the level of the output.
Methods:
Simulate the problem:
Information:
LSODAR.get_options()
Returns the current solver options.LSODAR.get_supports()
Returns the functionality which the solver supports.LSODAR.get_statistics()
Returns the run-time statistics (if any).LSODAR.get_event_data()
Returns the event information (if any).LSODAR.print_event_data()
Prints the event information (if any).LSODAR.print_statistics()
Prints the run-time statistics for the problem.