how to differentiation code,?

RJS
2022 2 1
1 个回答
更新时间：2022 2 3
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i want to wirte x*(1+s) into matlab function block in c code
wher x is input signal and s - is s laplace i.e. use for differentation in matlab
please help

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回答（1 个）

Benjamin Thompson
编辑：Benjamin Thompson 2022-2-1

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If you have x as sampled signal in time, differentiation is easy: (x(t2) - x(t1)) / (t2 - t1)

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RJS
RJS 2022-2-1
Thanks @Benjamin Thompson for your answer but how to perform this into matlab funtion block,
I tried but it's not working
Benjamin Thompson
编辑：Benjamin Thompson 2022-2-1
Simulink has blocks for differentiating signals. If you are using a continuous time signal, use the Derivative block in the Continuous library. If you are using discrete time signals, use the Discrete Derivative block. You could probably use a MATLAB Function Block, but you need to store the previous value of the input signal which takes some work, and you need access to the value of the time step--see the help article "Define MATLAB Function Block Data" for more information on providing data to this type of block in Simulink.
RJS
RJS 2022-2-2
@Walter Roberson @Benjamin Thompson thanks i know how to use this Transfer function block and derivative blocks , but want to write (k*s+1) in c code and then i want to test this code with my simulink plant model using matlab function block
Walter Roberson
Walter Roberson 2022-2-2
Simulink Coder can generate code for a Transfer Function block.
Have you considered building the C code as a Level 2 S-Function instead of calling it from a MATLAB Function Block ?
LaPlace notation is used for convenience to work with differential equations algebraically, for analysis or simplification, solving for parameters, etc. If you want a time based numerical solution to a differential or difference equation, you must convert to the time representation. In the case of differentiation that is fairly trivial.
Walter Roberson
Walter Roberson 2022-2-3
For any given numeric k, you can construct the numeric tf(), and use c2d() to find the equivalent discrete transfer function, the coefficients of which can be used to filter()
I just spent a while tracing through c2d, as I expected that there might be a relatively simple conversion for this case of 1/(k*s+1) .
Unfortunately, the internal construction of ss form involves a 2^round(log2(sqrt(1/k))) to construct a scaling factor, which makes the conversion a bit more complicated.
I kept looking through anyhow, thinking that at least in theory that might not be necessary, that you might be able to proceed with state space a=-1/k, b = 1, c = 1/k, d = 0, e = [] .
Sadly, inside the routine to discretize from zero order hold, there is a call to the undocumented mex routine matscale
I see hints that maybe you could use
Phi = exp(-Ts/k)
Gamma = k - k*exp(-Ts/k)
and
x[n+1] = Phi * x[n] + Gamma * u[n]
but I am not sure how that would translate into filter() or conv()

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