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Speed Up Simulation

Several factors can slow simulation. Check your model for some of these conditions.

  • The model includes an Interpreted MATLAB Function block. When a model includes an Interpreted MATLAB Function block, the MATLAB® execution engine is called at each time step, drastically slowing down the simulation. Use the Math Function block whenever possible.

  • Your model includes a MATLAB file S-function. MATLAB file S-functions also call the MATLAB execution engine at each time step. Consider converting the S-function either to a subsystem or to a C-MEX file S-function.

  • Your model includes a Memory block. Using a Memory block causes the variable-order solvers (ode15s and ode113) to reset back to order 1 at each time step.

  • The maximum step size is too small. If you changed the maximum step size, try running the simulation again with the default value (auto).

  • Your accuracy requirements are too high. The default relative tolerance (0.1% accuracy) is usually sufficient. For models with states that go to zero, if the absolute tolerance parameter is too small, the simulation can take too many steps around the near-zero state values. See the discussion of this error in Maximum order.

  • The time scale is too long. Reduce the time interval.

  • Your model represents a stiff system, but you are using a nonstiff solver. Try using ode15s. For more information, see Stiffness of System.

  • Your model uses sample times that are not multiples of each other. Mixing sample times that are not multiples of each other causes the solver to take small enough steps to ensure sample time hits for all sample times.

  • The model contains an algebraic loop. The solutions to algebraic loops are iteratively computed at every time step. Therefore, they severely degrade performance. For more information, see Algebraic Loop Concepts.

You can check the model blocks for the following conditions:

  • Your model feeds a Random Number block into an Integrator block. For continuous systems, use the Band-Limited White Noise block in the Sources library.

  • Your model contains a scope viewer that displays too many data points. Try adjusting the viewer property settings that can affect performance. For more information, see Scope Viewer.

  • You need to simulate your model iteratively. You change tunable parameters between iterations but do not make structural changes to the model. Every iteration requires the model to compile again, thus increasing overall simulation time. Use fast restart to perform iterative simulations. In this workflow, the model compiles only once and iterative simulations are tied to a single compile phase. See How Fast Restart Improves Iterative Simulations for more information.

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