[GEMPAK #NSV-394471]: GEMPAK - POIS diagnostic function

> Institution: Ohio State University
> Package Version: GEMPAK 5.8.3a
> Operating System: Fedora Linux
> Hardware Information: i686 athlon i386
> Inquiry: I'm looking for more information about the POIS diagnostic funtion, 
> to solve a Poisson equation.  Can you tell me about the numerical methods 
> used by the function to solve the equation (some kind of relaxation 
> technique?)  Also, how should the boundary values be specified, if there are 
> different boundary values for the top, sides and bottom of the domain (or is 
> this possible?)  Any additional information on this function would be 
> appreciated.  Thank you for your help!
> 
> Daniel Steinhoff
> 
> 
> 
> 

Daniel,

The POIS function is a 2-d function. You can see the actual code in the
source distribution $GEMPAK/source/gemlib/pd/pdslvp.c in the
current distribution. From the code itself: 

 * pd_slvp                                                              *
 *                                                                      *
 * This subroutine solves a Poisson equation by successive over-        *
 * relaxation.  The boundary conditions are assumed to be set in the    *
 * GES grid.  If ITYPBC is zero, Dirichlet boundary conditions apply    *
 * and the solution is done over all interior grid points.  If ITYPBC   *
 * is one, Dirichlet boundary conditions apply but the solution is done *
 * over all points interior to the two outer boundary points.  This     *
 * preserves the tangential and normal derivatives set up in the        *
 * GES grid.                                                            *
 *                                                                      *
 * The convergence criterion is that the average magnitude of the       *
 * residual be less than two percent of the average magnitude of the    *
 * forcing function.                                                    *
 *                                                                      *
 * Note:  This calculation is done only on the whole grid--no grid      *
 *        subsetting is allowed.

The mathematical expression is shown in $NAWIPS/doc/User_guide/pdf/apxB2.pdf.

Steve Chiswell
Unidata User Support

Ticket Details
===================
Ticket ID: NSV-394471
Department: Support GEMPAK
Priority: Normal
Status: Closed