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

Question

Sid Halder 2019-12-18

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https://ww2.mathworks.cn/matlabcentral/answers/497233-saving-output-values-from-a-function-into-an-array-to-plot-later

评论： Sid Halder 2019-12-18

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   

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Answer 1

Allen 2019-12-18

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https://ww2.mathworks.cn/matlabcentral/answers/497233-saving-output-values-from-a-function-into-an-array-to-plot-later#answer_406975

编辑：Allen 2019-12-18

在 MATLAB Online 中打开

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

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Sid Halder 2019-12-18

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.

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Answer 2

Cameron B 2019-12-18

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https://ww2.mathworks.cn/matlabcentral/answers/497233-saving-output-values-from-a-function-into-an-array-to-plot-later#answer_406978

在 MATLAB Online 中打开

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;