how to set vpasolve to only give positive solutions in matlab

To set vpasolve to only give positive solutions in MATLAB, you can use the assume function. Here's an example:

main.m
syms x
assume(x, 'positive')
eqn = x^2 -  4;
sol = vpasolve(eqn, x);
69 chars
5 lines

In the above code, we are assuming that x is positive using the assume function. This tells MATLAB to consider only positive values for x when solving the equation eqn. The vpasolve function then finds the positive solutions for x.

Note that using assume affects the entire MATLAB session, so make sure to reset assumptions using syms x or symsreset if you need to change the assumption later in your code.