ODE Integrators

PDESOL contains two state-of-the-art ODE integrators which compute solutions in accordance with a user-specified error tolerance:

(1) RKF45 - implementation of the Runge Kutta (RK) Fehlberg formulas (a fourth-order RK embedded in a fifth-order RK). The integrator is explicit, and therefore is intended for nonstiff ODEs.

(2) LSODES - implementation of backward differentiation formulas (BDFs), with variation of both the order of the BDF method and the integration time step. The integrator has a nonstiff option (mf = 10, where "mf" denotes the "method flag") and a stiff option (mf = 222).

In addition, PDESOL offers a fixed step EULER integrator which is particularly useful for debugging. A modified EULER routine is also included for use when the step size for the above integrators is constrained because of a small output interval.

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