E.g., vectorized code using logical indexing:
y = zeros(size(x));
g = x <= 0;
y(g) = cos(x(g));
y(~g) = sin(x(~g));
And for the 2nd set:
y = zeros(size(x));
g1 = x < 30;
g2 = x >= 30 & x < 50;
g3 = x >= 50;
y(g1) = cos(x(g1));
y(g2) = sin(x(g2));
y(g3) = x(g3).^2;
