# plot symbolic function real part

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john_arle on 31 Mar 2019
Commented: Star Strider on 31 Mar 2019
Hello there,
I would like to plot the real part of this symbolic function I have just solved.
Parameters 'a' and 'e' are varying between 5 and 9, and 0.05 and 0.15 respectively.
Unfortunately, it does not work.
Here you go with my code ( solution is a ratio of sum of Bessel functions of order zero).
clc
clear
set(groot,'DefaultAxesFontSize',14)
set(groot,'DefaultLineLineWidth',1.5)
syms a e
A = [besselj(0,-1i*a*e), bessely(0,-1i*a*e); ...
besselj(0,-1i*a), bessely(0,-1i*a)];
b = [-1; -1];
X = linsolve(A, b);
disp(X)
a = linspace(5,9);
e = linspace(0.05, 0.15);
plot(a, e, X)

Star Strider on 31 Mar 2019
You are plotting a function of two variables, so you need to use a plot that accommodates them, and that your function is symbolic.
Try this:
syms a e
A = [besselj(0,-1i*a*e), bessely(0,-1i*a*e); ...
besselj(0,-1i*a), bessely(0,-1i*a)];
b = [-1; -1];
X = linsolve(A, b);
disp(X)
a = linspace(5,9);
e = linspace(0.05, 0.15);
fsurf(real(X), [5 9, 0.05 0.15])
xlabel('a')
ylabel('e')
Experiment to get the result you want.

john_arle on 31 Mar 2019
Thank you. Any other options that fsurf that I can try?
regards,
Andrea.
Star Strider on 31 Mar 2019
As always, my plesure.
There are several 3D plots that will probably work with your system. See the documentation on fcontour (link), fmesh (link), and fplot3 (link).