function NumMeth2
    hold on
    h = 0.5;
    L = 50;
    x0 = 0;
    v0 = 2;
    y0 = 1
    x = []; y = [];
    x = x0:h:L;
    N = length(x);
    y(1) = y0;
    y(2) = y0 + h*v0 + h^2*ff(x0, y0, v0)/2;
    for j=2:N-1
        y(j+1) = 2*y(j) - y(j-1) + h^2*ff(x(j), y(j), (y(j) - y(j-1))/h);
    end
    plot (x, 0*x, 'k', x, y, 'r', 'LineWidth', 2)
        function u = ff(x, y, z)
            u = -4*sin(y)% - z/2;%u = -4*y + sin (2*x);
        end

end

