34.3 Usage

To include the RK integration tool into your FLASH development, add the line

REQUIRES numericalTools/RungeKutta

into the Config file of the directory where the global API's of the interpolation unit will be used. Another way would be to include the option

-with-unit=numericalTools/RungeKutta

into your command line when you configure the code with setup. This gives you access to the following RK tools:

• RungeKutta_step: Performs one unconfined RK step. Optimum stepping size is calculated internally by using equation 34.6 and readjusted until target accuracy is met. The routine requires as input an initial step size to start the RK stepping process.
• RungeKutta_stepConfined: Performs one confined RK step. Same underlaying machinery as for the unconfined RK stepper, except stepping size is additionally readjusted to comply with the supplied boundaries of the confined dependent variables.
• RungeKutta_stepSizeEstimate: Returns an estimate for initial step sizes in situations where no good initial guess of step size is available. The code is based on equations 34.10, 34.14 and 34.20.