Plot Fourier Series from a variable

I have this program which calculates the Fourier Series of a function. In this case the function is just f(t)=x. It makes the calculation correctly, and it can compute as many terms of the series as I want (in this case only 5 terms). However, I can not plot the series because the whole series is stored in the variable sys_sum. Can someone please help me plotting the series?

Code:

clc; clear all; close all;

syms x k L n

evalin(symengine,'assume(k,Type::Integer)');

%Obtain an and bn

a = @(f,x,k,L) int(f*cos(k*pi*x/L)/L,x,-L,L);

b = @(f,x,k,L) int(f*sin(k*pi*x/L)/L,x,-L,L);

%Fourier Series is calculated

fs = @(f,x,n,L) a(f,x,0,L)/2 + ... %a0/2 a0=an in the interation number 0 [k or n = 0]

symsum(a(f,x,k,L)*cos(k*pi*x/L) + b(f,x,k,L)*sin(k*pi*x/L),k,1,n); %+an*cos(nwt)+bn*sin(nwt)

f = x %Function

pretty(fs(f,x,5,pi)); %fs(f(t), x, n, T) ----- fs(function, variable x, number of terms, period)

sys_sum = fs(f,x,5,pi);

Answer 1

[Paul]

The easiest way would be to use fplot(). Also, use assume() instead of evalin

syms x k L n
% evalin(symengine,'assume(k,Type::Integer)');
assume(k,'integer')
assume(n,'integer')
%Obtain an and bn
a = @(f,x,k,L) int(f*cos(k*pi*x/L)/L,x,-L,L);
b = @(f,x,k,L) int(f*sin(k*pi*x/L)/L,x,-L,L);
%Fourier Series is calculated
fs = @(f,x,n,L) a(f,x,0,L)/2 + ... %a0/2    a0=an in the interation number 0 [k or n = 0]
    symsum(a(f,x,k,L)*cos(k*pi*x/L) + b(f,x,k,L)*sin(k*pi*x/L),k,1,n); %+an*cos(nwt)+bn*sin(nwt)
f = x %Function

f = 

x

pretty(fs(f,x,5,pi)); %fs(f(t), x, n, T) ----- fs(function, variable x, number of terms, period)

sin(3 x) 2              sin(4 x)   sin(5 x) 2
---------- - sin(2 x) - -------- + ---------- + 2 sin(x)
     3                      2           5

sys_sum = fs(f,x,5,pi);
fplot(sys_sum)