How can I plot laplace transformed functions?

How can I plot laplace transformed functions? Since the function should be imaginary I can not use fplot, can I? For example, how would I plot this:

syms x

f = sin(x);

l = laplace(f);

Thanks in advance.

[Paul]

syms x
f = sin(x);
l = laplace(f)

l = 

l is a function of complex variable, s. So it depend on what kind of plot you want to make.

[Murloc50]

I think a 3D Plot would be best since it is a function with a complex and real part, wouldnt it? Since I am no expert, what kind of plot would you recommend? Or does this depend on the function laplace() returns?

Answer 1

[Star Strider]

It might be easier to do this outside the Symbolic Math Toolbox.

That aside, try this —

syms x s js rs sigma omega
f = sin(x);
l = laplace(f)

l = 

lc(sigma,omega) = subs(l,{s},{sigma+1j*omega})                  % Define As Complex, With Complex Arguments

lc(sigma, omega) = 

figure
fsurf(lc, [ -0.1 0  -2*pi 2*pi ], 'MeshDensity',125)
xlabel('\sigma')
ylabel('\omega')
set(gca, 'YTick',[-2*pi :  pi/2 : 2*pi], 'YTickLabel',compose('%.1f\\pi',(-2:0.5:2)))
axis([-0.1 0.1  -2*pi 2*pi])

Plotting it in two dimensions is of course an option, however the function has three dimensions (,amplitude) so a three-dimensional plot is appropriate. The two complex-conjugate poles at are clearly visible.

Not perfect, however the best fsurf can do here with this function!

.

[Murloc50]

Thanks! This helped a lot.

[Star Strider]

As always, my pleasure!

.