[FLASH-USERS] Assertion failed in file ch3u_buffer.c

[Klaus Weide]

On Fri, 5 Dec 2014, niloofar afsari wrote:

> I'm trying to run Sod test with Uniform Grid with +nofbs option in FLASH4.2.
> So I set these values in flash.par:
> iGridSize = 8   #defined as nxb * iprocs
> jGridSize = 8
> kGridSize = 1
> iProcs = 4 #number or procs in the i direction
> jProcs = 2
> kProcs = 1 

You are requesting a grid of total size 8*8 cells, and dividing it across 
8 processes such that each process handles only a block of 2*4 ( 
iGridSize/iProcs * jGridSize/jProcs) cells. Clearly this resulting block 
size is too small to make sense.

Blocks are surrounded by NGUARD layers of guard cells, in your case NGUARD 
is 4 (by default), and the number of interior cells in each direction 
should be at least 2*NGUARD.  So

  iGridSize/iProcs >= 2*NGUARD
  jGridSize/jProcs >= 2*NGUARD

is violated in your case. [The factor of 2 may not be strictly needed
with +nofbs, but I don't think block sizes of less than 8 cells in any 
direction make much sense in FLASH anyway.]

I believe (but have not tested) that this can result in the kinds of 
errors you see; or worse, you could get undetected data corruption in some 
situations.

Klaus