Adaptive Runge-Kutta method for ordinary differential equations.

The embedded methods are designed to produce an estimate of the local truncation error of a single Runge-Kutta step, and as result, allow to control the error with adaptive step-size. This is done by having two methods in the tableau, one with order p and one with order $$p-1$$.

The lower-order step is given by

$y^*_{n+1} = y_n + h\sum_{i=1}^s b^*_i k_i,$

where the $$k_{i}$$ are the same as for the higher order method. Then the error is

$e_{n+1} = y_{n+1} - y^*_{n+1} = h\sum_{i=1}^s (b_i - b^*_i) k_i,$

which is $$O(h^{p})$$. The Butcher Tableau for this kind of method is extended to give the values of $$b_{i}^{*}$$

$\begin{split}\begin{array}{c|cccc} c_1 & a_{11} & a_{12}& \dots & a_{1s}\\ c_2 & a_{21} & a_{22}& \dots & a_{2s}\\ \vdots & \vdots & \vdots& \ddots& \vdots\\ c_s & a_{s1} & a_{s2}& \dots & a_{ss} \\ \hline & b_1 & b_2 & \dots & b_s\\ & b_1^* & b_2^* & \dots & b_s^*\\ \end{array}\end{split}$
Parameters
• f (callable) – The derivative function.

• show_code (bool) – Whether show the formatted code.

• dt (float) – The numerical precision.

• tol (float) – The error tolerence.

• var_type (str) – The variable type.

__init__(f, var_type=None, dt=None, name=None, adaptive=None, tol=None, show_code=False, state_delays=None, neutral_delays=None)[source]#

Methods

 __init__(f[, var_type, dt, name, adaptive, ...]) build() load_states(filename[, verbose]) Load the model states. nodes([method, level, include_self]) Collect all children nodes. register_implicit_nodes(nodes) register_implicit_vars(variables) save_states(filename[, variables]) Save the model states. set_integral(f) Set the integral function. train_vars([method, level, include_self]) The shortcut for retrieving all trainable variables. unique_name([name, type_]) Get the unique name for this object. vars([method, level, include_self]) Collect all variables in this node and the children nodes.

Attributes

 A B1 B2 C arg_names arguments All arguments when calling the numer integrator of the differential equation. dt The numerical integration precision. integral The integral function. name neutral_delays neutral delays. parameters The parameters defined in the differential equation. state_delays State delays. variables The variables defined in the differential equation.