ABSTRACT
When a simulation diagram is complete, as in Fig. 6-19, to run it you go to the main menu bar and select SIMULATION and then PARAMETERS. A dialog box appears where you select start time (generally 0), stop time (to suit your problem),
integrator type (use RK-5 for most problems), and minimum and maximum computing step size. The RK-5 integrator is a variable-step-size type, but I generally start every new simulation with a fixed step size, only going to the variable-step feature after I am sure that I am getting reasonable results. To force the RK-5 integrator to be fixed-step, just enter the max and min step sizes as the same value. Choose the step size to be about 1/1000 or 1/2000 of the total problem time if you have nothing else to go on. If oscillations of known frequency are expected, make the step size about 1/ 10 of the oscillation period. Once you are getting reasonable results, you should increase and decrease the step size to make sure you are in a range where halving or doubling step size seems to have no effect on the results. If you let RK-5 decide on the step size and how it changes during a run (by making max and min step sizes different numbers), watch out for large step sizes which may give accurate points, but "jagged" graphs because of coarse point spacing.
