[FLASH-BUGS] Multipole gravity broken in parallel?

[Sean Couch]

Hi,

I am having trouble implementing the multipole gravity solver on  
multiple processors.  I am using a 2D spherical grid with periodic  
boundary conditions in theta and outflow BCs in radius.  I am using  
isolated grav BCs.  I have tested the setup on a single processor and  
it works fine.

The error seems to be that initial values for the gravitational  
potential are not calculated correctly.  The grav potential will  
typically be accurate up to a certain radius, after which the value  
of the potential becomes negative infinity.  This 'cut-off' radius is  
number-of-processors dependent.  Generally increasing the number of  
processors increases the cut-off radius, however using 128 processors  
still gives the same error, regardless of domain size!  This problem  
with the potential immediately leads to a non-convergence in the  
Riemann solver on the first time step.

I am running Flash 2.5 on an Intel Linux cluster using Intel  
compilers.  I have had plenty of success with the identical setup,  
neglecting self-gravity, on numerous processors.  Also, point mass  
gravity works without a hitch.  I have also tried the sedov 
+selfgravity problem, which uses the multipole solver in spherical  
coordinates, and I get the very same error.  I would try the multgrid  
solver, but that is not supported for spherical coordinates.

Any help would be very much appreciated,
Sean