[Users] Error in GRHydro_SlopeLimiter.F90

Ian Hawke I.Hawke at soton.ac.uk
Tue Jan 10 05:05:41 CST 2012

On 09/01/12 20:47, Joshua Faber wrote:
> Hi everyone,
>    I believe the routines in GRHydro_SlopeLimiter.F90 are all either 
> mislabelled or simply the wrong formulae.  As a quick reminder, for  
> the upwind slope ("dupw") and downwind slope ("dloc"), we expect to 
> get the following results:
> On the rather nice wikipedia page, 
> http://en.wikipedia.org/wiki/Flux_limiter
> they take variables r = dupw/dloc and phi = delta / dloc, but the 
> results are the same.
Assuming the ET files follow Whisky, then I would note:

1) The Whisky results follow from my thesis, which follow from Toro (1st 
2) Toro gives a formula to convert Flux limiters to Slope limiters; they 
are _not_ the same thing in his notation. The flux limiters are the 
canonical values, but the slope limiters "corresponding" to the flux 
limiters use different formulas.
3) I didn't revisit them after implementation, and it should be noted 
that Toro fixed a large number of typos between 1st and 2nd edition, so 
it wouldn't surprise me if some followed through.

Saying all that, is there really a great call for the slope limiters? I 
would have thought that minmod and MC (the correct version is MC2) would 
be enough for basic testing. I've had similar thoughts with the Roe 
solver in the past; only inertia and not wanting to redo testsuites 
stopped me from taking them out of Whisky ages ago. Why not just remove 
them? Less to maintain, especially if they're not used.


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