[Simulink/Matlab] How to access variable from M-file?

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Natt 2011-10-3

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Greetings!

I created a model that does channel coding and it employs bpsk and channel repetition.

I have 3 variables that are inputs. snr, rep, frame_size

Where snr is signal to noise ratio, rep is number of repetitions, and frame_size is, well, the frame_size. This isn't really important but figured I would paint a picture...

I want to perform an analysis where I try to find the bit error rate (ber) while varrying the signal to noise ratio and repetitions--for each frame size.

From the command line, I set the snr, rep, and frame_size. Let's say my model is called channel_coding, I then run sim('channel_coding').

Low and behold ber pops up because it is set to go to the workspace as a variable called ber in the model.

So, I want to write a little script that collects all of this data while varying the parameters I mentioned. However, if I set the variable in the m-file, the model doesn't know and if I set the variable at the command line the m-file doesn't know but the model does.

I have tried making the variables snr, rep, and frame_size 'global'. That didn't work.

I also tried using simset() and that didn't work.

So, my friends. Would someone please share with me this secret that the bowels of the internet is hiding from me?

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Fangjun Jiang 2011-10-3

What is "Low and behold ber pops up"?

Natt 2011-10-3

@Fangjun Jiang

1) "How are the three variables snr, rep and frame_size used in the model? Are they used by any blocks as parameters?"

--snr: snr is used as the signal to noise ratio value in the AWGN block

--rep: rep is used as the number of times to repeat each bit (for repetition coding) in a custom subsystem block

--frame_size: frame_size is used as the parameter for the Bernoulli binary generator

So, before I run my model, I set each of these variable values in the base workspace.

2) What is "Low and behold ber pops up"?

ber: ber is the 1x3 row vector that is the output of the error rate calculation.

In a clean workspace, with only snr, rep, and frame_size set, ber is the output to the workspace after the model runs.

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回答（1 个）

Fangjun Jiang 2011-10-4

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在 MATLAB Online 中打开

In that case, I don't see any reason why you can't run the following script, just an example:

all_snr=rand(10,1);
all_rep=1:10;
all_frame_size=10:10:100;
result=zeros(10,3);
for k=1:10
snr=all_snr(k);
rep=all_rep(k);
frame_size=all_frame_size(k);
sim('channel_coding');
result(k,:)=ber;
end

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Natt 2011-10-4

@Fangjun Jiang

"If you run the simulation manually (not using sim() command), after the simulation is completed, do you see ber in the base workspace?"

--If I run the simulation by pressing the play button in Simulink, I do see the variable ber in the base workspace.

"Is your script inside a function? I assume you know the difference between M-function and M-script."

--My script is inside a function called channel_coding.

I do know that my function has its own workspace, if that's what you mean. Is this my problem? Here is the code:

function ber_plot()

% We are going to end up making a plot of BER v SNR to each of the four

% frame sizes.

%snr = -6:1:10; % increase in 1 dB increments, up to 10 dB

%rep = 1:2:9; % increase in 2 bit increments, up to 9

% Make a separate plot for each frame size, but keep the variance of the

% other paramters the same for each case of frame size. So there will be

% a total of 4 plots.

frame_size = 64; % sequence = 64, 16, 128, 256

bit_err = [0 0 0];

for i = 1:4

switch i

case i == 2

frame_size = 16;

case i == 3

frame_size = 128;

case i == 4

frame_size = 256;

otherwise

frame_size = frame_size;

end

for j = -6:1:10

snr = j;

for k = 1:2:9

rep = k;

sim('channel_coding');

% need to create 4 different bit_err arrays for each frame size

bit_err = [bit_err; ber]

end

Natt 2011-10-4

@Kaustubha Govind

That's the ticket! Thanks!

Fangjun Jiang 2011-10-4

Use simset() is a better solution if your MATLAB version support that. Try to use that as much as you can. Then you don't need to change from M-function to M-script anymore.

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