Discrete Problems

Mathematical Specification of a Discrete Problem

To define an Discrete Problem, you simply need to give the function $f$ and the initial condition $u₀$ which define a function map:

\[u_{n+1} = f(t,u_n)\]

f should be specified as f(t,u) (or in-place as f(t,u,du)), and u₀ should be an AbstractArray (or number) whose geometry matches the desired geometry of u. Note that we are not limited to numbers or vectors for u₀; one is allowed to provide u₀ as arbitrary matrices / higher dimension tensors as well.

Note that if the discrete solver is set to have scale_by_time=true, then the problem is interpreted as the map:

\[u_{n+1} = u_n + dtf(t,u_n)\]

Problem Type

Constructors

DiscreteProblem(f,u0,tspan) : Defines the discrete problem with the specified functions.

Fields

f: The function in the map.
u0: The initial condition.
tspan: The timespan for the problem.
callback: A callback to be applied to every solver which uses the problem. Defaults to a black CallbackSet, which will have no effect.

Note About Timing

Note that if no dt and not tstops is given, it's assumed that dt=1 and thus tspan=(0,n) will solve for n iterations. If in the solver dt is given, then the number of iterations will change. And if tstops is not empty, the solver will revert to the standard behavior of fixed timestep methods, which is "step to each tstop".