- class scipy.integrate.RK23(fun, t0, y0, t_bound, max_step=inf, rtol=0.001, atol=1e-06, vectorized=False, first_step=None, **extraneous)#
Explicit Runge-Kutta method of order 3(2).
This uses the Bogacki-Shampine pair of formulas . The error is controlled assuming accuracy of the second-order method, but steps are taken using the third-order accurate formula (local extrapolation is done). A cubic Hermite polynomial is used for the dense output.
Can be applied in the complex domain.
Right-hand side of the system: the time derivative of the state
t. The calling signature is
fun(t, y), where
tis a scalar and
yis an ndarray with
len(y) = len(y0).
funmust return an array of the same shape as
y. See vectorized for more information.
- y0array_like, shape (n,)
Boundary time - the integration won’t continue beyond it. It also determines the direction of the integration.
- first_stepfloat or None, optional
Initial step size. Default is
Nonewhich means that the algorithm should choose.
- max_stepfloat, optional
Maximum allowed step size. Default is np.inf, i.e., the step size is not bounded and determined solely by the solver.
- rtol, atolfloat and array_like, optional
Relative and absolute tolerances. The solver keeps the local error estimates less than
atol + rtol * abs(y). Here rtol controls a relative accuracy (number of correct digits), while atol controls absolute accuracy (number of correct decimal places). To achieve the desired rtol, set atol to be smaller than the smallest value that can be expected from
rtol * abs(y)so that rtol dominates the allowable error. If atol is larger than
rtol * abs(y)the number of correct digits is not guaranteed. Conversely, to achieve the desired atol set rtol such that
rtol * abs(y)is always smaller than atol. If components of y have different scales, it might be beneficial to set different atol values for different components by passing array_like with shape (n,) for atol. Default values are 1e-3 for rtol and 1e-6 for atol.
- vectorizedbool, optional
Whether fun may be called in a vectorized fashion. False (default) is recommended for this solver.
vectorizedis False, fun will always be called with
n = len(y0).
vectorizedis True, fun may be called with
(n, k), where
kis an integer. In this case, fun must behave such that
fun(t, y)[:, i] == fun(t, y[:, i])(i.e. each column of the returned array is the time derivative of the state corresponding with a column of
vectorized=Trueallows for faster finite difference approximation of the Jacobian by methods ‘Radau’ and ‘BDF’, but will result in slower execution for this solver.
P. Bogacki, L.F. Shampine, “A 3(2) Pair of Runge-Kutta Formulas”, Appl. Math. Lett. Vol. 2, No. 4. pp. 321-325, 1989.
Number of equations.
Current status of the solver: ‘running’, ‘finished’ or ‘failed’.
Integration direction: +1 or -1.
Previous time. None if no steps were made yet.
Size of the last successful step. None if no steps were made yet.
Number evaluations of the system’s right-hand side.
Number of evaluations of the Jacobian. Is always 0 for this solver as it does not use the Jacobian.
Number of LU decompositions. Is always 0 for this solver.
Compute a local interpolant over the last successful step.
Perform one integration step.