Special note: The fixed sample time is available only if the Periodic sample time constraint is set to Unconstrained. However, it should be noted that if the model contains only continuous states, the re-harness resets the tick period on the transform to be the default as described above in case 2. Note that in practice, the LCD value returned follows the same rules as if the fundamental sample time is set to that value as described above in case 1 (the user CAN change the value, but it is not recommended, since it either ticks the S‑Function needlessly or misses transitions).Īny change to any sample period requires a re-harness of the model.
If the model contains periodic sample times (via discrete blocks, for example), Matlab reports the least common denominator (LCD) of the specified sample times, and that is the value that is used. The default is the 50 equal steps (or 0.2), however the user can change to whatever you want for the run.ģ. However, by virtue of the fact that the S‑Function block is a discrete block, the tick period specified in the Transform is the fundamental sample time used by the model. If the model does not define any periodic sample times (it only contains continuous states), Matlab chooses a step size that divides the total simulation into 50 equal steps (if the simulation is set to run Inf, this time is 0.2). When the fundamental sample time is set to auto the following occurs:Ģ. (which, by ticking at a greater rate, would miss things). The user can change the tick period in the transform to 0.001 (which would unnecessarily tick the S‑Function at 2 times out of 3) or 0.006, 0.009, etc. In this case, the default tick period is 0.003. For example, if the fundamental sample time is set to 0.003, you can have blocks of 0.003, 0.006, 0.009, but NOT blocks of 0.003, 0.005, 0.009 since 0.005 is not divisible integrally by 0.003. When the fundamental sample time is not set to auto, all discrete steps specified in the model (sample times in blocks, etc.), must be an integral multiple of the fundamental sample time. Always initialize the tick rate to be the value that Matlab returns as the lowest fixed period. Note that there can be more than one, since there may be multiple rates in the model. When harnessing the model, the model is compiled to determine the fixed sample times.
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