# Plotting Step Responses with For Loops

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N/A am 24 Jan. 2015
Kommentiert: N/A am 25 Jan. 2015
Hi, I have a problem with the plot command in regards to plotting step responses in for loops. I've searched everywhere and cannot find what I'm looking for. I am hoping someone can help me. Here's my problem:
I need to plot a simple step response over a series of different time constants. It's a first order system with time constant ranging from 35 over multiples of 5 to 60, and it begins at 25 and ends at 100 (it's a temperature problem).
Here's my code:
>> for tau=35:5:60,
sys=tf([75],[tau 1]);
y=25+step(sys);
plot(y)
hold on
end
And with that, all I get is one curve using the last tau of 60. And that's the value MATLAB stores even though I told it to keep 35-->60. If I use just "step(sys)", I get all my curves. I think it has something to do with the plot command. Any help is appreciated--thank you in advance!!
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### Akzeptierte Antwort

Rick Rosson am 25 Jan. 2015
figure;
axes;
hold on;
for tau = 35:5:60
sys = tf([75],[tau 1]);
[y,t] = step(sys);
plot(t,25+y);
end
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N/A am 25 Jan. 2015
Yes! Thank you so much! I wonder why the loop didn't hold for my code? Because if I would just directly use
step(sys)
hold on
end
...everything works (except the 25 increase at the beginning). Either way, now it works, so thank you!

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