How to create a meaningful loop to meet certain conditions

Hi there,

I want to create a loop function that sets the value of xA according to a vector A = linspace(100,150,51). Respecting the current value of xA, xB shall be used for computation along a certian delta, like (300 <= xB <=350) and with a step size of 1. By the way, xA and xB are just scalars.

After xA and xB are defined, a set of equations is solved. Then, the results of these solved equations are compared to each other. If all results are equal within a tolerance, the loop is ended and the respecting values of xA and xB are displayed. If the results are not equal (within tolerance) the values of xA and xB are changed as described above.

If I had any idea how to solve this I would show you my code - but since I am newbie, it would make no sence to present something.

Thanks a lot for any helpful comment!!!

Answer 1

[Ameer Hamza]

Something like this perhaps,

A = 100:1:150; % for fixed spacing, this syntax is more readable
B = 300:1:350;

for i = 1:numel(A)
    xA = A(i);
    for j = 1:numel(B)
        xB = B(j);
        % solve the equation here
        if abs(sol1-sol2)<1e-6 % compare two numbers with tolerance
            fprintf('Solution is xA=%.f and xB=%f\n.', xA, xB);
            break; % break the loop
        end
    end
end

[Mirko Mißbach]

What a quick response, thx! I will let you know after I've implemented the equations. One question, how do I compare three results for equality?

abs(sol1-sol2)<1e-6 & abs(sol1-sol3)<1e-6 ???

[Ameer Hamza]

Yes, this condition seems fine. Another way is to check the standard deviation (or variance) of the three solutions

if std([sol1 sol2 sol3]) < 1e-6

[Mirko Mißbach]

Thank you, both variants work. Unfortunatelly I have just identified another problem which forces me to incorporate a further "requirement".

Within the range of A and B there are solutions with positive and negative values for sol1 sol2 and sol3 (like: sol1 < 0; sol2 > 0 and sol3 < 0 ...). But there is at least one solution in which sol1 sol2 and sol3 are all positive or all negative! How can I smartly incorporate this requirement right before equality check?

Thanks again for helpful comments :)

[Ameer Hamza]

If you want to make sure that three numbers have same sign, you can try something like this

all(diff(sign(x))==0)