Mellin representation of the completed Riemann zeta function (source code)

= Mellin representation of the completed Riemann zeta function
{c}

For $\Theta(u)=\sum_{n\in\mathbb Z}e^{-\pi n^2u}$ and initially $\Re s>1$,
$$
\pi^{-s/2}\Gamma(s/2)\zeta(s)
=\frac12\int_0^\infty(\Theta(u)-1)u^{s/2}\frac{du}{u}.
$$
The <Poisson summation formula> gives $\Theta(u)=u^{-1/2}\Theta(1/u)$. Splitting the integral at one therefore continues it meromorphically and makes its invariance under $s\mapsto1-s$ visible.