The function return value might be unset error

[Walter Roberson]

The message appears to be correct to me. You do not store anything into a variable named sol anywhere inside calcall. What value should be returned by the function?

Answer 1

[Image Analyst]

You don't seem to use sol, so just get rid of it:

function calcall(t)

Or else set it to something

function sol = calcall(t)
sol = zeros(1, 4); % Initialize it to something in case of error afterwards.
% Computations for ave, mx, mn, st ... then
sol = [ave, mx, mn, st];

or whatever you want to return.

And disp() displays in the command window, not onto the figure you created.