[FLASH-BUGS] ppm/kurganov test differences

[Sean Matt]

Hello again,

	We have recently been testing and comparing the ppm and kurganov
hydro solvers, and we've encountered an interesting problem.  
Specifically, we are running the standard sod problem in setups/sod.
We setup with:

setup sod -auto -maxblocks=1000

And, we are running on Tru64 (OSF1 V5.1) using a Compaq fortran compiler
(V5.5-1877-48BBF).  

	We can run the standard run with ppm (without modifying
"flash.par" or any other files) and get a result that is consistent with
the true sod solution.  However, when we make only one change to the
Config file to select the kurganov solver, the computed solution is wrong
by exactly a factor of two.  The change we make to Config is to replace
the line:

REQUIRES hydro

with:

REQUIRES hydro/explicit/delta_form/kurganov

Then, of course, we rerun the setup command and recompile.  We make no
changes to the flash.par file (except to basenm for a different file
name).  I've attached two gif's of 1-d slices in density of the solutions,
so that you can see the error.  ppm.gif is the solution from ppm and
kurg.gif is the solution from the kurganov solver, and each are from the
final checkpoint file at a physical time of t=0.2.  As you may know, the
true Sod problem solution looks the same at different times, but one
simply has to rescale the x-axis proportional to time.  It is quite
interesting and baffling that the kurganov solution is off by exactly a
factor of two.  That is, if you rescale the x-axis of the kurganov
solution by a factor of two, it would then match with the ppm.  In other
words, the kurganov solution is behaving as though everthing is moving at
half speed.

Have we done something wrong?  It is worth noting that we have also
compared the two solvers for the standard sedov setup, and the shock speed
is the same for both solvers (i.e., both solvers give the "right"  
answer, in that setup).


		-Sean


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