[FLASH-BUGS] possible bugs in Poisson routines

[Artur Gawryszczak]

Hi,

I've attached two setups derived from dust_coll, which shows quite strange 
results.

In both cases I'm using "natural" units, so G*density = 1, and box walls are 
set at +/-1

dust_coll.2d_cart_mgrd - sets up a collapse on 2-D cartesian grid using 
multigrid submodule. Everything works fine, except that free-fall time is 
longer than expected for given initial density. It takes 0.5 unit of time to 
collapse, while in my opinion it should take 1/sqrt(2*pi) (this is a collapse 
of an infinite cylinder). I've tried to run this problem in 3D, changed 
init_block.F90 to fill a cylinder instead of sphere and put periodic BC in 
z-direction. The free-fall time did not change.

dust_coll.3d_cart_mpol - sets up a collapse on 3-D cartesian grid using 
multipole submodule. Strange bubble forms at the center of the sphere when 
"mpole_lmax" parameter is set high enough, i.e. 10 or more. 
-- 
Best Regards
Artur
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