Are you trying to plot the addition of two sinusoidal functions, 
even when there are discontinuities?
even when there are discontinuities?x = linspace(-1, 1, 2001);
a = 1;
b = 1;
k = pi;
m = pi;
d = 0;
f = sin(k*x);
g = cos(m*x + d);
fp = f.*(f > 0);
gn = g.*(g < 0);
% Plot
subplot(221)
plot(x, f), grid on, ylim([-1.5 1.5]), title({'$f(x)$'}, 'interpreter', 'latex')
subplot(223)
plot(x, g), grid on, ylim([-1.5 1.5]), title({'$g(x)$'}, 'interpreter', 'latex')
xlabel({'$x$'}, 'interpreter', 'latex')
subplot(222)
plot(x, fp, x, gn), grid on, ylim([-1.5 1.5]), title({'$f^{+}(x)$ and $g^{-}(x)$'}, 'interpreter', 'latex')
legend({'$f^{+}(x)$', '$g^{-}(x)$'}, 'interpreter', 'latex', 'location', 'northwest')
subplot(224)
plot(x, fp + gn), grid on, ylim([-1.5 1.5]), title({'$f^{+}(x) + g^{-}(x)$'}, 'interpreter', 'latex')
xlabel({'$x$'}, 'interpreter', 'latex')
