[Carpet] Error when using moving grids

[Erik Schnetter]

On Aug 23, 2006, at 15:44:39, Yosef Zlochower wrote:

>> I take back my statement that there should be no time interpolation.
>> In order to fill the past time levels during regridding, Carpet  
>> has  to
>> interpolate in time.  With prolongation_order_time=0, Carpet uses   
>> only
>> 1 time level to do so, namely the current time level -- and that   
>> means
>> that this "interpolation" has to occur at just the time of that  time
>> level.
>
> I don't understand why Carpet would need to interpolate in time.
> Data on current and past time levels can  be obtained by spatial
> interpolation only.

I call in "time interpolation" because this is a generic expression.   
In your case, the interpolation happens to be exact.

If you specify an nth order time interpolation, then Carpet uses the  
most current n+1 time levels to interpolate.  This could be changed  
-- Carpet could instead choose some other set of time levels for its  
interpolations -- but it is unambiguous.

In your case, Carpet needs to fill in the past time level with data  
only from the current time level.  That is not an interpolation any  
more, it is an extrapolation, which is why Carpet complains.

>> I think you should set the order of time interpolation to a value
>> corresponding to the number of time levels which you use.  I  
>> assume  you
>> use 2 time levels, hence using linear interpolation would be   
>> adequate.
>> Try prolongation_order_time=1.
>>
>> -erik
>>
>
> I get a similar error with 1st order prolongation
>
> WARNING level 0 in thorn CarpetLib processor 0 host master
>    (line 1680 of
> /home/yosef/NCactus/Cactus_New/configs/carpetmol/build/CarpetLib/ 
> data.cc):
>    -> Internal error: extrapolation in time.  time=-1  times=[1,0]

Do you get this error with the exact parameter file that you sent  
earlier, except that you changed the prolongation order in time?

-erik

-- 
Erik Schnetter <schnetter at cct.lsu.edu>

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