Add 2 trigonometric functions, with conditions

Greeting to all,

I am trying to add graphically 2 trigonometric functions:

1. f(x)=a*sin(k*x), graphicaly displayed only for positive value (≥0)
2. g(x)=b*cos(m*x+d), graphicaly displayed only for negative value (≤0)

Thanks

Answer 1

[Sam Chak]

Are you trying to plot the addition of two sinusoidal functions, 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')

Answer 2

[Panagiotis Arvanitis]

Thank you Sam Chak,

Yes, I am trying to add two functions with discontinuities.

I didn't get the same output graph, both positive and negative values appeared.

x  = linspace(-0.5, 4, 2001);
a  = 1;
b  = 1;
k  = pi;
m  = pi;
d  = 0.25;
f  = sin(k*x);
g  = cos(m*x + d);
% Plot
plot(x, f, x, g, x, f+g), grid on, ylim([-2 2])
xlabel({'$x$'}, 'Interpreter', 'LaTeX'), 
ylabel({'$y$'}, 'Interpreter', 'LaTeX'), 
legend({'$x$'}, 'Interpreter', 'LaTeX', 'FontSize', 14, 'Location', 'Northwest')

[Sam Chak]

Hi @Panagiotis Arvanitis

I have fixed the code in my Answer.

Please check if that that is the signal desired.

Answer 3

[Panagiotis Arvanitis]

Hi @Sam Chak

I appriciate your hepl!!. It works

Thank you