# Not sure how to fix my matrix dimension problem

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Erik Sharrer on 29 Mar 2020
Edited: Adam Danz on 29 Mar 2020
t=0:0.1:4
m=5;
k=1000;
zeta=[0, 0.1, 0.25, 0.5, 0.75, 0.9, 1];
xo=0.05;
vo=0;
w=sqrt(k/m)
wd=w*sqrt(1-zeta.^(2))
A=(sqrt((vo+zeta.*w.*xo).^(2)+(wd.*xo).^(2))).*(1./wd)
o=atan((xo*wd).*(1./(vo+zeta*w*xo)))
figure(1)
for i=1:length(zeta)
x=A.*exp(-w*zeta.*t).*sin(wd.*t+o);
plot(t,x)
hold on
end

Adam Danz on 29 Mar 2020
Edited: Adam Danz on 29 Mar 2020
t is a 1x41 vector; wd and zeta are both 1x7 vectors. You can't do pairwise multiplication with two arrays of different size.
Base on the line plot(t,x) I assume you are expecting t to have the same number of elements as x in which case t will also need to be a 1x7 vector.
Perhaps you're looking for
t = linspace(0,4,numel(zeta));
or
t = cumsum([0, 0.1 * ones(1,numel(zeta)-1)]);
But there's another problem/mystery: you're not using the i variable within your loop and the values for x will never change within the loop so you'll end up plotting the same line over and over again.
##### 2 CommentsShowHide 1 older comment
Adam Danz on 29 Mar 2020
Edited: Adam Danz on 29 Mar 2020
The cumsum() results in the same step size as your original t vector but extends to a 0.6 instead of 4.
The linspace() results in values between 0 and 4 just like your original t vector but with different step sizes.

MaryD on 29 Mar 2020
You are using for loop with variable i but you are not using i inside the loop. I'm not sure what you want to achive but maybe this will work
for i=1:length(zeta)
x=A(i).*exp(-w*zeta(i).*t).*sin(wd(i).*t+o(i));
figure(i)
plot(t,x)
hold on
end
Adam Danz on 29 Mar 2020
Edited: Adam Danz on 29 Mar 2020
If you're plotting all of that on the same figure, move figure(1) and hold on outside of the loop (see my previous comment). Also, move title(), xlabel(), and ylabel() outside of the loop (before or after).
I also recommend you label the lines so you know which one is which.
for i = _____
x = ______
plot(t,x, 'DisplayName', num2str(i))
end
legend()