Why does NextTimeHit always return 0 in Matlab S-Functions?

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retigi 2018-7-3

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/408551-why-does-nexttimehit-always-return-0-in-matlab-s-functions

回答： Archit Dhanani 2019-7-25

I need to compute the step size (i.e. dt) in the discrete update method of a Matlab S-Function whose Sample Time is set to be "Inherited" (i.e. [-1 0]). However, regardless of the Sample Time specification (e.g. Inherited, Continuous, Discrete, Variable), the "block.NextTimeHit" always return "0" even though it is decleared as R/W in its Matlab Documentation.

Why does NextTimeHit always return 0 in Matlab S-Functions?
How can I infer the actual step size in update method of (Discrete) Matlab S-Functions for inherited and variable sample times?

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Answer 1

Archit Dhanani 2019-7-25

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https://ww2.mathworks.cn/matlabcentral/answers/408551-why-does-nexttimehit-always-return-0-in-matlab-s-functions#answer_384840

the NextTimeHit is the API used specifically for variable discrete rates. You can read more about it in the page:

https://www.mathworks.com/help/simulink/ug/types-of-sample-time.html#brrdmmw-11

To get the actual step size used in the update method, you will have to use Dwork vectors. The link below demonstrates an example for using Dwork vectors:

https://www.mathworks.com/help/simulink/sfg/writing-level-2-matlab-s-functions.html#brgtux6