MATLAB Answers

Saving output values from a function into an array (to plot later)

3 views (last 30 days)
Sid Halder
Sid Halder on 18 Dec 2019
Commented: Sid Halder on 18 Dec 2019
So I have written a loop that runs a function for a given m to give a specific time_hours value (for that given m). The program works and I get all the values I need, but how would I save these values in an array to plot against m later on? I'm not sure how this would work as I have used fzero to calculate the time_hours values on each iteration and fzero values cannot be indexed? Thanks for any help, here is my code:
alpha = 0.7e-7; rho = 0.1 .^(1/3); %m = [4:0.1:8];
for m = 4:0.1:8
[term, scarysum, summation_t, f, time_seconds, time_hours] = tcalc(alpha, rho, m);
end
function [term, scarysum, summation_t, f, time_seconds, time_hours] = tcalc(alpha, rho, m)
scarysum = 0;
for k = 1:30
syms t
term = ((-1).^(k-1))./k .* sin(k.*pi.*rho) .* exp((-1 .* k.^2 .* pi.^2 .*alpha.*(1360.*pi).^(2/3).*t)./m.^(2/3));
scarysum = scarysum + term;
end
summation_t = matlabFunction(scarysum);
f = @(t) (2./(pi*rho) .* (summation_t(t))) - 0.7125;
time_seconds = fzero(f,14400);
time_hours = time_seconds ./ 3600;
disp(time_hours)
end

  0 Comments

Sign in to comment.

Accepted Answer

Allen
Allen on 18 Dec 2019
Edited: Allen on 18 Dec 2019
If your function is returning scalar values that are being overwritten during each iteration of your for-loop, try the following as a replacement to your for-loop.
[term, scarysum, summation_t, f, time_seconds, time_hours] = arrayfun(@(m) tcalc(alpha, rho, m), 4:0.1:8);
% This is essentially the same as rewriting the for-loop to something like this, which changes the size
% of the output variables each iteration and appends the new value to the end of each variable.
rng = 4:0.1:8;
for m = length(rng)
[term(m), scarysum(m), summation_t(m), f(m), time_seconds(m), time_hours(m)] = tcalc(alpha, rho, rng(m));
end

  1 Comment

Sid Halder
Sid Halder on 18 Dec 2019
Thank you so much! It's honestly so convenient that arrayfun exists, perfect function to use in my case. Ran into a few problems with arrayfun as my output variables contained exponential terms (which aren't scalar) so MATLAB had issues creating the new arrays but I think I've sorted it all out. Thanks once again.

Sign in to comment.

More Answers (1)

Cameron B
Cameron B on 18 Dec 2019
options = optimset('PlotFcns',@optimplotfval);
scarysum = 0;
for k = 1:30
syms t
term = ((-1).^(k-1))./k .* sin(k.*pi.*rho) .* exp((-1 .* k.^2 .* pi.^2 .*alpha.*(1360.*pi).^(2/3).*t)./m.^(2/3));
scarysum = scarysum + term;
end
summation_t = matlabFunction(scarysum);
f = @(t) (2./(pi*rho) .* (summation_t(t))) - 0.7125;
[time_seconds,fval,exitflag,output] = fzero(f,14400,options);
time_hours = time_seconds ./ 3600;
disp(time_hours)
fig = gcf;
dataObjs = findobj(fig,'-property','YData');
y1 = dataObjs(1).YData;
x1 = dataObjs(1).XData;
You'll have to save y1 and x1 each time, but that's how you'd extract the data.

  0 Comments

Sign in to comment.

Tags

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!