function f = funcion_rectangular (x)
    [n,m]=size(x);
    f = zeros(n,m);
    intervalo_1 = find(x>=0 & x< 1.5);
    intervalo_2 = find(x>=1.5 & x <= 3);
    f(intervalo_1)=3;
    f(intervalo_2)=0;
endfunction