POISSX, Poisson Equation on Rectangle with Various Boundary Condition

1 - Nature of physical problem solved: The subroutine POISSX solves the Poisson equation on a rectangle with either Dirichlet, Neumann or periodic boundary conditions. More precisely, the program solves the linear equation system which arises when the differential equation is discretized on a rectangular grid with m inner grid points in the x and n points in the y direction using second order finite difference approximations. The values of m and n must be larger than one but are otherwise arbitrary. For more details see the references and the comment cards included in POISSX. The main program and the subroutine case provided with POISSX set up 36 cases to test POISSX. 2 - Method of solution: The solution is obtained by cyclic reduction; see references