#範例11-7：求週期函數f(x)=|x|，在(-pi < x < pi)的傅立葉級數Fourier Series
from sympy import *
x = symbols('x')
f = Function('y')(x)
f = abs(x)
#傅立葉級數
s = fourier_series(f, (x, -pi, pi))
fs = s.truncate(n=8)

#畫圖
plot(fs, line_color='red')