1D Burgers equation pseudo-spectral solver

				du   1  d               d^2
				-- + -- -- (u*u) = nu * ---- (u)
				dt   2  dx              dx^2

The analytical solution considered is

			u(x,t) = 4 - 2 * nu * d/dx(phi(x,t)) / phi(x,0)

 where

			phi(x,t) = exp(-(x-4*t     ) / (4*nu*(t+1)))
				 + exp(-(x-4*t-2*pi) / (4*nu*(t+1)))

Periodic boundary conditions are considered for a [0,2*pi] domain

			u(0,t) = u(2*pi,t)

The FFTW3 library is required for the FFT and IFFT transforms.
The gfortran command to compile in Ubuntu: $ gfortran burgers1d.f90 -I/usr/include -lfftw3 -o burgers1d
Distributed under the GNU GENERAL PUBLIC LICENSE.

Author: B. Font Garcia
October 2016