MATLAB Answers


Why is my variable not staying updated in Simulink

Asked by Nicholas on 18 Jun 2013


I am using Simulink and have a variable set to zero in an enabled subsystem. I send the signal out of the subsystem and am trying to update it as x = x + 1 where x is the signal. After simulink goes through all the blocks once and gets back to where x = x + 1 the x is reset to 0. I have a breakpoint in the enabled subsystem where I initialized it and it never goes back there. Any ideas would be appreciated. Thank you!


Could you please explain what block(s) you use to implement the x=x+1 part?

I am using MatLAB Function blocks. For a simplified example I am using a Matlab function block in the enabled subsystem that defines x = 0; Then I output the signal to the input of another MAtLAB function block outside of the subsystem where x = x + 1; I have a pulse generator for the enable of the subsystem

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2 Answers

Answer by Nicholas on 19 Jun 2013
 Accepted Answer

Actually, I think I figured out what I needed to do. So I declared x as global and found the data store memory block. After I found the block I found Thank you very much for your time and interest in helping me.


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Answer by Erwin Torreao Dassen on 18 Jun 2013
Edited by Erwin Torreao Dassen on 18 Jun 2013

Is this a custom matlab function block? In that case try declaring the variable persistent. (UPDATED)


It is using MatLAB Function blocks. I'm new to MAtlab and am unfamiliar with persistent. I tried it in the subsystem and got an error that outputs can't be persistent. I tried it in the other function block and it says persistent must precede all use of a variable.

I'm not sure I understand what you trying to achieve. My guess of what is happening is that your matlab-function block that defines x = 0 is being used as input outside the subsystem. If that is the case the first block outside this subsytem will always receive 0 as input signal and it will never output more than 1... In fact, your matlab-function block is just a "constant" block.

What is the behavior you want to obtain?

Regards, Erwin

Thank you for your response. Yes my output is being used outside the subsystem as an input. So the overall goal is that I have a model where I want to measure a signal that goes to my MatLAB function block. Whenever the signal is zero and the simulation reaches that function block I want x to add one and be used as a counter. After the signal is zero for a certain amount of times through and the counter gets so high I want the output of my function block to change. I guess basically I'm not sure how to initialize a variable in simulink. Everytime Simulink's simulation reaches the end of all my blocks it wraps around and starts over again. So when I initialize the signal earlier on the simulation resets the value to 0 again. I thought I'd fixed the problem with the enabled subsystem block but apparently not. Thank you again.

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