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I'm brand new to Matlab, and have created a very simple function here to calculate an ion's equilibrium potential:

function y = equipotent(n,X1,X2)

y = (58/n) * log10(X1/X2);

I'd like to do two things: 1) vary X2 for a set of values (1-100) while keeping X1 and n constant. and 2) store all the outputs from the function in a vector for plotting X2 vs y.

Anything helps! Thanks!

the cyclist
on 14 Apr 2014

If you change your code to

function y = equipotent(n,X1,X2)

y = (58/n) * log10(X1./X2);

then it will give a vector output y for vector input X2, and you should be all set.

Sven
on 14 Apr 2014

Hi Derek,

MATLAB has some useful ways to do what you're trying to do. If you use the (.*) operator instead of (*), it will perform a vector multiplication.

Therefore you can adjust your function as follows:

function y = equipotent(n,X1,X2)

y = (58 ./ n) .* log10(X1 ./ X2);

Then you can just run commands:

y = equipotent(4, 3, X2)

figure

plot(X2,y)

Did that help you out?

Sven
on 14 Apr 2014

Ah, this sounds like the following code would help you:

n = 4;

X2 = (1:100)'; % Let's make it a vertical (100-by-1) vector

X1_set = 1:5; % Let's use 5 different values for X1

% So the result(s) can be collected in a 100-by-5 matrix

y_set = zeros(length(X2), length(X1_set));

for i = 1:length(X1_set)

y_set(:,i) = equipotent(n, X1_set(i), X2);

end

% And plot them

figure

plot(X2,y_set)

legend(num2str(X1_set'))

I'll update my answer accordingly. Is this what you were looking for?

Note that in your original question:

2) store all the outputs from the function in a vector for plotting X2 vs y

You only wanted to plot X2 (which is a 100-length vector) against y. In the original answer, putting the (.*) operator in the function lets you calculate y all-at-once so that y is also a 100-length vector. There should have been no need to run your function more than once.

In my comment above I've also showed how to store sets of y for different input via a loop. This is the only time where you'd need to run your function more than once (and therefore need to avoid overwriting your previous answer by putting y into columns of the y_set matrix.

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