[FLASH-USERS] Resistive MHD question

[Robert Fisher]

Dennis :

   Obtaining negative mass densitites is a classic signature of a numerical 
instability -- you are advecting more mass out of a cell in a timestep 
than it has in total.

   This can happen in a few different ways, but the most common problem 
(barring major bugs) is that you are using an timestep criterion which is 
not sufficient.

   How have you generalized CFL in this case?

   Also, note that CFL is itself not sufficient if the accelerations are 
large, or if there is sudden heating in the system.

   Best wishes,

   Bob