How to plot for different values of parameters on one run?

Asked by parag gupta

parag gupta (view profile)

on 30 Jul 2019
Latest activity Commented on by parag gupta

parag gupta (view profile)

on 2 Aug 2019
Accepted Answer by David K.

David K. (view profile)

How to get the plots for different values of aplha = 2,3,4,5 on one run and how to merge all those graphs ?
function [t,y] = call_dstate()
tspan = [0 9]; % set time interval
y0 = 10; % set initial condition
% dstate evaluates r.h.s. of the ode
[t,y] = ode45( @dstate ,tspan ,y0);
plot(t,y)
disp([t,y]) % displays t and y(t)
function dydt = dstate (t,y)
alpha=2; gamma=0.0001;
dydt = alpha* y-gamma *y^2;
end
end

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Answer by David K.

David K. (view profile)

on 30 Jul 2019

Matlab actually has a page on this called Parameterizing Functions.
Using one of the options for that I believe this will do it for you. This works because the nested function can use variables created in the outer function.
function [t,y] = call_dstate()
tspan = [0 9]; % set time interval
y0 = 10; % set initial condition
% dstate evaluates r.h.s. of the ode
gamma=0.0001;
for alpha = 2:5
[t,y] = ode45( @dstate ,tspan ,y0);
plot(t,y); hold on;
end
disp([t,y]) % displays t and y(t)
function dydt = dstate (t,y)
dydt = alpha* y-gamma *y^2;
end
end

parag gupta

parag gupta (view profile)

on 2 Aug 2019
Thanks! How I will get to know which graph in the plot is for alpha = 2 and which one for alpha = 5?
I have attached the graph I got by running the above code.
David K.

David K. (view profile)

on 2 Aug 2019
I may be wrong but it looks like you chose a color for the plot to use. So first I would suggest letting it choose a different color for each. Or if you want to do it manually you can create an array to set them yourself like this
color = {'r','m','b','c'}
for alpha = 2:5
[t,y] = ode45( @dstate ,tspan ,y0);
plot(t,y,color{alpha-1}); hold on;
end
Then you can add a legend after they are all plotted like this
for alpha = 2:5
...
end
legend('a=2','a=3','a=4','a=5')
And a legend will show up indicating which color plot corresponds to each alpha
parag gupta

on 2 Aug 2019
Thanks david 😁