[FLASH-USERS] The better the grid accuracy, the more fluctuations and instability may occur in the calculation results

[Hansen, Eddie]

Answers to Ryan’s questions would certainly be helpful, but I suspect that the MPI issue could be that with a uniform grid setup, you need to set iProcs and jProcs in your par file such that iProcs*jProcs is equal to the number of processors you’re trying to use with the mpirun command (I’m assuming a 2D sim).

--
Eddie Hansen
Applications Group Leader
Flash Center for Computational Science


From: flash-users <flash-users-bounces at flash.rochester.edu> on behalf of Ryan Farber <rjfarber at umich.edu>
Date: Friday, June 21, 2024 at 11:03 AM
To: lizy <3287940670 at qq.com>
Cc: flash-users <flash-users at flash.rochester.edu>
Subject: Re: [FLASH-USERS] The better the grid accuracy, the more fluctuations and instability may occur in the calculation results
Hi Lizy,

It would be helpful if you can provide more information to give you more direct help :)

Can you share the MPI error? Probably you need to set the path to your MPI installation in your /PATH/TO/FLASH/sites directory.
Regarding higher resolution producing randomly distributed data - what's your Simulation_initBlock look like? Are you in fact generating random variables?

Best,
--------
Ryan


On Thu, Jun 20, 2024 at 8:55 PM lizy <3287940670 at qq.com<mailto:3287940670 at qq.com>> wrote:

Dear Flash Developer,

I used two types of uniform grids, - nxb=256- nyb=128 and - nxb=128- nyb=56, respectively, but the results of the calculations were very different. The results of the more precise grid calculations were actually very inaccurate, and the density and other data were randomly distributed. What is the reason?

In addition, I want to use multi-core operations. After setting it in flash. par, I entered mpirun - np 2 flash 4.8 but encountered an error. Should this command be performed before the ./setup command?

Thank you very much for your answer

Lizy
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