# Using for loop to plot multiple plots on the same graph

5 views (last 30 days)
RPS19 on 2 Apr 2021
Commented: RPS19 on 2 Apr 2021
I am trying to plot 3 plots on the same graph , I believe the best way to do this would be a for loop. I'd like to keep the paramaters that I am changing flexible, so I would like to call them from an array. This is the code that I have so far, where 'Tau1' is a parameter that varies the function 'G_fun'. I am only getting one plot which the legend is labelling to be the last plot with Tau1 = 1e-5. How would I be get a different plot of G_fun for each value of Tau1 on the same graph? Thank you in advance for any help.
N = [1e-3,1e-4,1e-5];
for i = 1:1:3
Tau1 = N(i); % the parameter to be changed
if N(i) == 1e-3
figure
hold on
end % end if
bode(G_fun);
end
hold off
legend('Tau1 1e-3', 'Tau1 1e-4', 'Tau1 1e-5')
grid on
title('System Bode Plots')
DGM on 2 Apr 2021
What is G_fun? How is it getting the parameter Tau1?

DGM on 2 Apr 2021
Edited: DGM on 2 Apr 2021
I'm going to guess the primary issue is with your function not getting access to the changing parameter, but let's just show that it does work. There are a few things that can be improved:
% i just changed these to suit my example TF
N = [2e-1,1e-1,1e-2];
% you can just move this outside the loop to avoid the conditional
figure
hold on
legendstrings=cell(size(N));
for i = 1:length(N) % make stuff independent of array sizes
Tau1 = N(i);
% idk what your TF is or how tau is used in it
% this is just some garbage i made as an example
H = tf([1 0.1 7.5*(1-Tau1)],[1 0.12 9 0 0]);
bode(H)
% build the legends from the parameters themselves
% instead of using literal strings that might be wrong if N changes
legendstrings{i}=sprintf('Tau1 = %2.2e',Tau1);
end
hold off
legend(legendstrings,'location','northwest') % you can just set the location as needed
grid on
title('System Bode Plots')
RPS19 on 2 Apr 2021
Thank you! This is a much better way of doing it, much more flexible which is what I needed. The problem was with my function not getting access to the variables. I had G_fun = G(a,b,c,Tau1) where G() is my actual transfer function. When I inputted G() instead of G_fun within the for loop it worked perfectly, although I don't completely understand why.

William Rose on 2 Apr 2021
Try putting the figure command and the hold on command outside and before the for loop.