[FLASH-USERS] Patch for a bug fix for USM-MHD solver in FLASH3.3 & FLASH4 releases

[dongwook at flash.uchicago.edu]

Dear Flash users,

I've found that one bug has been accidently introduced and released in two
previous FLASH releases. The affected versions are FLASH3.3 and
FLASH4-alpha.

The bug affects calculations of electric fields which are used to update
cell-face divergence-free magnetic fields on a staggered grid. This
applies only to AMR runs, and UG calculations should't get affected by
this bug.

In most of cases, the effects are very small, but may introduce some
incorrect evolutions of magnetic fields, especially for high beta-plasmas.

Please find attached two routines for FLASH3.3 and FLASH4, and replace
the old ones with them:

 * hy_uhd_unsplit.F90.bugFixed.flash3.3
 * hy_uhd_unsplit.F90.bugFixed.flash4

Please let me know if you any questions. Thank you!

Best regards,
Dongwook

=========================================
Dongwook Lee, Ph.D., Research Scientist
FLASH Center for Computational Science
University of Chicago
5747 S. Ellis Ave., Room 319
(773) 834-6830

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