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A sawtooth function in the interval of length \(L=1\)`\begin{align}
f(x) ~=~ \begin{cases} -x, &\mbox{} \left(0,~ \frac{1}{2}\right) \\
1-x, &\mbox{} \left(\frac{1}{2},~ 1\right) \end{cases}
\end{align}`is approximated here by two different Fourier series:`\begin{align}
f(x) ~=~ \underset{n}{\boxed{+}} ~ \frac{1}{ \mathrm{i}\,2\pi\,n } \, \text{e}^{\mathrm{i}\,2\pi\,n\, (x-1/2)}
\end{align}`

The not so good approximation (red) is the Fourier series terminated at \(n_{\text{max}}=1\). The better approximation (blue) is the Fourier series terminated at \( n_{\text{max}} = 20 \).