In your function, you could just extract the elements of coef into your a, b, and c variables if you wanted to. E.g.,
function roots = my_quadratic_formula(coef)
a = coef(1);
b = coef(2);
c = coef(3);
:
% then your code that uses a, b, c, goes here
And then assign the outputs:
roots(1) = _______; % <-- you fill in this code
roots(2) = _______; % <-- you fill in this code
