Represent Simulink Integrator block as Matlab Function

2012 12 4
5 个回答
回答已采纳
更新时间：2020 8 10
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1 个投票

Hi.
I need to implement the following behavior :
The Integrator and my_Integrator blocks have to be equivalent I/O.
How should I write the Matlab Function ?
Thanks for any reply.

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Ryan G
Ryan G 2012-12-4

1 个投票

As this looks like a homework problem, I can't answer directly. However I will point you in the direction of persistent variables.

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Azzi Abdelmalek
Azzi Abdelmalek 2012-12-7
编辑：Azzi Abdelmalek 2012-12-8

2 个投票

I don't know why do you need this, maybe if you explain exactly what you need, there is better way

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River Rock
River Rock 2012-12-8
The model diagram should be as light as possible, as shown in the first attached picture: one input and one output, no additional simulink blocks.
River Rock
River Rock 2012-12-8
Sure we can. Ryan's idea works.
Would it be easier to use a S-function instead of a MATLAB Function ?
Azzi Abdelmalek
Azzi Abdelmalek 2012-12-8
编辑：Azzi Abdelmalek 2012-12-8
It works with Ryan's hint, but you still need a clock as an input.
River Rock
River Rock 2012-12-8
编辑：River Rock 2012-12-8
The solution it's already posted above. But since you and Guy disapprove this, I am waiting for the better solution.
I didn't need any clock input , please see http://www.mathworks.com/matlabcentral/answers/55705-represent-simulink-integrator-block-as-matlab-function#comment_115977
And even if I did, I guess it could have been fetched using the get_param command (never tried this though)
Azzi Abdelmalek
Azzi Abdelmalek 2012-12-8
编辑：Azzi Abdelmalek 2012-12-8
Ok, I see, If T is constant, you must then set, in model configuration parameters your fixed step time to T, and also your step block sample time to T. In this case you don't need a clock.
function y = fcn(u)
persistent uold yold
T=0.01;
if isempty(uold)
uold=0;yold=0;
end
y = u*T+yold-(u-uold)*T/2
yold=y;uold=u;
River Rock
River Rock 2012-12-8
Changing the sample time of the Step block to 0.01 removed the previous offset. Thanks

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Guy Rouleau
Guy Rouleau 2012-12-5

0 个投票

This is not a good idea. The MATLAB function is not designed for this purpose.

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Edward Rodriguez
Edward Rodriguez 2020-8-10
Excuse me, so, What would be a good idea to implement numerical integration methods in blocks in Simulink?

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River Rock
River Rock 2012-12-5
编辑：River Rock 2012-12-6

0 个投票

My main goal is to implement the differential equations of a physical system using a single Matlab Function. As the sums and gains were easy to represent, I couldn't find any alternative for the integration.

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Ryan G
Ryan G 2012-12-5
Why do you need to use MATLAB over SL blocks? Look into the persistent variables, it will get the job done, although as Guy mentioned, it's not the best way to do it.
River Rock
River Rock 2012-12-5
Your idea would be to declare a persistent variable for the numeric integration ?
Y(s) = U(s) / s => y(z) = yOld + u(z)
so you declare persistent x = y to stand for yOld ?
Can I avoid this low-level arithmetic and call a predefined method instead (ode45 for example) ?
Ryan G
Ryan G 2012-12-5
What you have written is close it would be more like:
y(z) = yOld+u(z)/SampleTime
You cannot use the ODE solver in the MATLAB function block.
River Rock
River Rock 2012-12-7
Any idea on how to get rid of this offset ?
http://i.imgur.com/cxr5H.png
Code looks like:
function y = fcn(u)
%#codegen
T=0.01;
persistent yOld;
persistent uOld;
if (isempty(yOld))
yOld = 0;
end
if (isempty(uOld))
uOld = 0;
end
y = yOld + (T/2)* (u + uOld);
%y=yOld + u*T;
yOld = y;
uOld = u;

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River Rock
River Rock 2012-12-5

0 个投票

Can anybody suggest a better way of implementing the numerical integration ? The code has to be written inside the Matlab Function Block though.

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