Control a Simulink module by an M-file

Hi, I need to change values in time in a simulink simulation, I tried first to do a simple example wich have a source and a resistance, I tried to change the value of the resistance with the following m-file:

z=100
set_param('test', 'SimulationCommand', 'start')

if tout > 3 
    z=10
end

I saw in other blogs that the "tout" is considered the time of the simulation. The simulation runs, but the resistance only takes the value of 100.

Can you please help me? It's probably something very simple I guess.

Answer 1

[Kaustubha Govind]

What you're doing with the command "set_param('test', 'SimulationCommand', 'start')" is the equivalent of hitting the "Play" button the model. The model simply logs "tout" to the MATLAB workspace as an array (not as a scalar). Also, there is no guarantee that tout is updated immediately during simulation - it is only guaranteed that at the end of simulation "tout" is a vector containing the list of all time-steps that the model ran at. Even if "tout" were a scalar and were updated instantly, the line "if tout>3" would have to run at the exact instant that tout became >=3. You probably need to put in some kind of while loop to be more realistic, but like I said, even a while loop will not help in this case.

What you might need to do instead is write something like a MATLAB Function that reads the simulation time value (perhaps from the Clock block) and performs the set_param. You can call this function from one of three MATLAB Function blocks so it is run at every simulation time-step. Alternatively, you could use a solution similar to this FEX submission.

[Nelson Silva]

Thank's for your help.

I tried to do it with the clock block with an s-function. But now I'm having a problem calling the function to the m-file. It says that is an undefined function.

[Kaustubha Govind]

Is the function you're trying to call on the MATLAB path?

[Nelson Silva]

I connected the clock block to the Fcn block and do nothing else to the function on the Fcn block, staing it like this:

function y = fcn(u)

% This block supports the Embedded MATLAB subset.

% See the help menu for details.

y = u;

Now I want to run the m-file calling the function but I can't, How should I name it in the the m-file?

[Kaustubha Govind]

Ah! You are using the MATLAB Function block, not the Fcn block. In any case, you should be able to call your function from that block. Just edit the function to do something like:

function y = fcn(u)

% This block supports the Embedded MATLAB subset.

% See the help menu for details.

y = callmyfunction(u);

[Kaustubha Govind]

Just saw that grapevine gave you a more extensive answer to your comment.

Answer 2

[grapevine]

You might use a clock block

http://www.mathworks.nl/help/toolbox/simulink/slref/clock.html

connected to a Matlab Fcn block,

http://www.mathworks.nl/help/toolbox/simulink/slref/matlabfunction.html

which is associated to a m-file, in my example I called it stopSimulation.m. Within this mfile I wrote this code

function [isTChanged] = stopSimulation(u)
if(u>3)
    set_param(gcs,'StopTime','4')
    isTChanged=1
else
    isTChanged=0
end

which is capable to change the simulation duration to 4 s after the first 3s

good luck

[Nelson Silva]

I connected the clock block to the Fcn block and do nothing else to the function on the Fcn block, staing it like this:

function y = fcn(u)

% This block supports the Embedded MATLAB subset.

% See the help menu for details.

y = u;

Now I want to run the m-file calling the function but I can't, How should I name it in the the m-file?

[grapevine]

you should replace the default code of the Matlab function block

"

function y = fcn(u)

% This block supports the Embedded MATLAB subset.

% See the help menu for details.

y = u;

"

with this one :

"

function [isTChanged] = stopSimulation(u)

if(u>3)

set_param(gcs,'StopTime','4')

isTChanged=1

else

isTChanged=0

end

"

that's all

for further details take a look at this doc

http://www.mathworks.nl/help/toolbox/simulink/ug/f6-106261.html

Answer 3

[Nelson Silva]

Thanks for all your answers, but I still can't do what I intend to. Now I tried to change the parameter of the resistance block with a variable in the parameter, and then give a value to this variable in the function block, but I still haven't resolve my problem. Can't anyone send me an example of what I pretende to my email or give any other ideia of how can I do that?

[Kaustubha Govind]

Do you see an error? Or did you mean that the parameter value isn't changing?

[Nelson Silva]

Yes I see an error, it gives an error on the variable in the resistance parameter.

[Kaustubha Govind]

Nelson: Could you please paste the exact error message?

[Nelson Silva]

the error is the following

Block error

Error in 'tresist/rc': Parameter 'z' cannot be evaluated. MATLAB error message: Undefined function or variable 'rr'.

[Nelson Silva]

the error is the following

Block error

Error in 'tresist/rc': Parameter 'z' cannot be evaluated. MATLAB error message: Undefined function or variable 'z'.

[Kaustubha Govind]

If using a variable called 'rr' to represent the value of the parameter, you need to define 'rr' with a numerical value in the workspace and say "set_param('tresist/rc', 'z', 'rr')".

Answer 4

[Albert Yam]

So you want to run the simulation, and have 'z' change from 100 to 10 at 3 seconds? Is 'z' a constant block? Change it to a Lookup-table (n-D), 1 table dimension

ts = 0.1; %timestep?
z.time = [0 3-ts 3 t_final]; %breakpoint set
z.signals.values = [100 100 10 10]; %table data
set_param('test', 'SimulationCommand', 'start')

Edit: You need a clock block into the Lookup-table.

[Nelson Silva]

'z' is the variable in the resistance parameter, what i want is to change the resistance value during the time.

[Albert Yam]

What are you using to load 'z' into the model? A constant block? From Workspace block? From File block? Signal Builder?

[Nelson Silva]

The problem is that, i can load 'z' into the model when the simulation is runing. I can only load it when the simulation is stoped by an m-file

[Albert Yam]

You still haven't answered the question, about what block you are using to load 'z'. Are you using a [resistor] block? I am guessing that works like a [constant block]. A [constant block] will NOT update while the simulation is running, so you have to use a different block. Use a [Variable Resistor], with an input. I suggested a lookup table, so that you can define beforehand,

from 0-3, set z = 100
from 3-t_final set z = 10

C.J.Harris's 'step' block also does this, and works in this manner.

Answer 5

[C.J. Harris]

You are all making this more complicated than it actually is. Use the 'Step' block. Set the initial value to '100', set the final value to '10', and then set the step-time to 3.

[Nelson Silva]

But that's not a resistance value (ohm), that only works as a signal and not what I intend to