  A new method is presented for solving Poisson's equation inside an open-ended
rectangular pipe. The method uses Fast Fourier Transforms (FFTs) to perform
mixed convolutions and correlations of the charge density with the Green
function. Descriptions are provided for algorithms based on the ordinary Green
function and for an integrated Green function (IGF). Due to its similarity to
the widely used Hockney algorithm for solving Poisson's equation in free space,
this capability can be easily implemented in many existing particle-in-cell
beam dynamics codes.
