Fourier coefficients : fourier_an and fourier_bn or fourier_cn

Let f be a T-periodic continuous functions on $\mathbb {R}$ except maybe at a finite number of points. One can prove that if f is continuous at x, then;

$${\frac{{a_0}}{{2}}} \sum_{{n=1}}^{{+\infty}} {\frac{{2\pi nx}}{{T}}} {\frac{{2\pi nx}}{{T}}}$$ f (x) =

$$\sum_{{n=-\infty}}^{{+\infty}} {\frac{}{}} \pi$$ =

where the coefficients a_n, b_n, n $\in$ N, (or c_n, n $\in$ Z) are the Fourier coefficients of f. The commandsfourier_an and fourier_bn or fourier_cn compute these coefficients.