Using Simulink

Improving Simulation Accuracy

To check your simulation accuracy, run the simulation over a reasonable time span. Then, reduce either the relative tolerance to 1e-4 (the default is 1e-3) or the absolute tolerance and run it again. Compare the results of both simulations. If the results are not significantly different, you can feel confident that the solution has converged.

If the simulation misses significant behavior at its start, reduce the initial step size to ensure that the simulation does not "step over" the significant behavior.

If the simulation results become unstable over time:

• Your system may be unstable.
• If you are using ode15s, you may need to restrict the maximum order to 2 (the maximum order for which the solver is A-stable) or try using the ode23s solver.

If the simulation results do not appear to be accurate:

• For a model that has states whose values approach zero, if the absolute tolerance parameter is too large, the simulation will take too few steps around areas of near-zero state values. Reduce this parameter value or adjust it for individual states in the Integrator dialog box.
• If reducing the absolute tolerances do not sufficiently improve the accuracy, reduce the size of the relative tolerance parameter to reduce the acceptable error and force smaller step sizes and more steps.

Speeding Up the Simulation

Running a Simulation from the Command Line