If you can calculate the vector components (i.e. directions) than you only have to arrange them into an array. Suppose that you have calculations for the single directions in functions f1, f2 and f3:
function F = vectorFunction(r, theta, phi)
% calculate the directions
F1 = f1(r, theta, phi);
F2 = f2(r, theta, phi);
F3 = f3(r, theta, phi);
% arrange directions in array (here: column vector)
F = [F1; F2; F3];
end
function out = f1(r, theta, phi)
out = r + theta + phi;
end
function out = f2(r, theta, phi)
out = r * theta * phi;
end
function out = f3(r, theta, phi)
out = r * theta - phi;
end
