FFT solver for Poisson equation
 

Hi All,
Iam simulating the swimming of an elastic filament in neutrally buoyant fluid using Immersed Boundary Method. Iam using a square periodic domain. The boundary conditions for pressure and velocity are periodic in both X and Y directions. Iam developing the code using Visual Fortran 90.
I have to use FFT for solving pressure poisson equation. I don;t have idea about how to use FFT in my code for periodic BC's.So plse tell me the procedures how I can use FFT in visual fortran 90 for solving pressure poisson equation with Periodic boundary conditions in X and Y directions.Plse tell me the step by step details as I don;t have idea about the use of FFT in fortran.
Anticipating a positive reply at the earliest......

Take a look at the DNS code at www.channelflow.org. It might give you idea on the development of the solver.