How to input multiple values to the same variable to avoid having to keep changing the values and rerunning the program each time?

Hello, I am trying to write a program that will output three different values based on three different input combinations, e.g. n1 = f(sigma_x1,sigma_y1,sigma_z1), n2 = f(sigma_x2,sigma_y2,sigma_z2), and n3 = f(sigma_x3,sigma_y3,sigma_z3).

Here is my attempt at doing that. How can I do this calculation without getting an error in the program? Thank you.

sigma_x = [100 200 300];
sigma_y = [400 500 600];
tau_xy = [700 800 900];

%--------------------------------------%

S_y = 350; % MPa (Given)

sigma_max_min_a = ((sigma_x+sigma_y)/2)+sqrt(((sigma_x - sigma_y)/2).^2+tau_xy.^2);

sigma_max_min_b = ((sigma_x+sigma_y)/2)-sqrt(((sigma_x - sigma_y)/2).^2+tau_xy.^2);

if sigma_max_min_a > 0 && sigma_max_min_b > 0
    if sigma_max_min_a > sigma_max_min_b
        sigma_max = sigma_max_min_a;
        sigma_min = 0;
    else
        sigma_max = sigma_max_min_b;
        sigma_min = 0;
    end
elseif sigma_max_min_a < 0 && sigma_max_min_b < 0
    if sigma_max_min_a < sigma_max_min_b
        sigma_max = 0;
        sigma_min = sigma_max_min_a;
    else
        sigma_max = 0;
        sigma_min = sigma_max_min_b;
    end
elseif sigma_max_min_a > 0 && sigma_max_min_b < 0
    sigma_max = sigma_max_min_a;
    sigma_min = sigma_max_min_b;
else
    sigma_max = sigma_max_min_b;
    sigma_min = sigma_max_min_a;
end

Operands to the logical AND (&&) and OR (||) operators must be convertible to logical scalar values. Use the ANY or ALL functions to reduce operands to logical scalar values.

n = S_y/(sigma_max - sigma_min)

[Jan]

Whenever you mention an error in the forum, include a copy of the complete message also. Please share this important information with the readers.

[Thomas Herlihy]

Okay, I have display the error message.

Answer 1

[Jan]

Do you get a message concering the && operators? They need scalars are inputs. If you provide vectors, use & .

But then

if sigma_max_min_a > 0 && sigma_max_min_b > 0    

has a vectors as condition. Because conditions of if commands must be scalars, Matlab inserts an all() implicitly. If you want to calculate the code for the 1st elements of sigma_x/y/z, then for the 2nd elements, usw. your code need more modifications.

The simple solution would be a loop.

sigma_x = [100 200 300];
sigma_y = [400 500 600];
tau_xy = [700 800 900];

result = zeros(1, 3);
for k = 1:3
    result(k) = f(sigma_x(k), sigma_y(k), tau_xy(k));
end

Vectorizing the code is useful, if you applie it for millions of values and speed matters. Then logical indexing is the way to go.

By the way, avoid name monsters like "sigma_max_min_a" and "sigma_max_min_". The code is small and the readability is higher, if you simply call them "a" and "b".

[Thomas Herlihy]

Alright, thanks for explaining that. This method is very useful.