[Users] CCTK_ReductionArrayHandle

[Luca Baiotti]

OK, Erik, but could you give advice on the correct and recommended way 
to get and use the handle as in the examples I gave?

A related question: do I understand correctly that the new API requires 
to activate LocalReduce in parfiles (if one uses Carpet), while 
CarpetReduce is no longer needed and so should not be activated?

Luca


On 8/3/12 8:40 PM, Erik Schnetter wrote:
> Luca
>
> I may have been confused. The flesh offers two different reduction
> APIs, one (the newer one) implemented by PUGH and LocalReduce, the
> other one (the older one) implemented by Carpet. I may have mixed up
> the names of the new and the old interfaces...
>
> -erik
>
> On Thu, Aug 2, 2012 at 10:26 PM, Luca Baiotti <baiotti at ile.osaka-u.ac.jp> wrote:
>> On 8/2/12 9:19 PM, Erik Schnetter wrote:
>>>
>>> On 2012-08-02, at 4:26 , Luca Baiotti <baiotti at ile.osaka-u.ac.jp>
>>> wrote:
>>>
>>>> On 8/2/12 4:11 PM, Roland Haas wrote:
>>>>>>
>>>>>> CCTK_ReductionArrayHandle is used in several thorns but it is
>>>>>> not described in the ReferenceManual. Is it (still) supported?
>>>>>> How is it different from CCTK_LocalArrayReductionHandle?
>>>>>
>>>>> It's part of the "old" reduction interface. Which happens to be
>>>>> the one Carpet supports, so it is widely used  :-). I doubt
>>>>> support will go away anytime soon. The calls are documented in
>>>>> the User manual in section C1.7.5 (page 84 in my build).
>>>>
>>>>
>>>> I see, so CCTK_ReductionArrayHandle is described in the User's
>>>> Manual but not in the Reference Manual.
>>>>
>>>>> As for differences I'd consult this section and the reference
>>>>> manual. It seems that one is a reduction over local arrays (ie
>>>>> double a[100]) while the other reduces grid functions (or grid
>>>>> arrays or grid scalars most likely).
>>>>
>>>>
>>>> I found no reference saying that CCTK_ReductionArrayHandle should
>>>> be used only for local arrays or only for grid functions.
>>>>
>>>> Which of the two codes below is correct (in a subroutine called by
>>>> the scheduler)? Why?
>>>
>>>
>>> For historic reasons, local reductions (where the caller passes in
>>> the grid size) and "regular" reductions (which use grid variables)
>>> have different operators. In principle, using the wrong operator
>>> should lead to an error message at run time.
>>>
>>> What happens currently is likely that PUGHReduce and CarpetReduce
>>> register the same operators for both local and global reductions in
>>> the same order, and (by coincidence!) their handles are thus
>>> interchangeable.
>>>
>>> Below, number (1) is correct, number (2) is wrong.
>>>
>>> Number (2) obtains a handle for a global reduction operation. This
>>> handle will have a certain value, e.g. 15. Later, the code uses the
>>> _local_ reduction operation with handle 15, which (apparently) is
>>> also the local sum reduction.
>>>
>>> We should correct this. For example, we could add large, different
>>> offsets for local and global handles, so that they would be
>>> different. We already do this for other integer IDs in the flesh.
>>>
>>> -erik
>>>
>>>> 1)
>>>>
>>>> CCTK_REAL local_array_in,local_array_out;
>>>>
>>>> CCTK_INT handle = CCTK_LocalArrayReductionHandle("sum");
>>>>
>>>> CCTK_ReduceLocArrayToArray1D(cctkGH, -1, handle, &local_array_in,
>>>> local_array_out, 4, CCTK_VARIABLE_REAL));
>>>>
>>>>
>>>> 2)
>>>>
>>>> CCTK_REAL local_array_in,local_array_out;
>>>>
>>>> CCTK_INT handle = CCTK_ReductionHandle("sum");
>>>>
>>>>
>>>> CCTK_ReduceLocArrayToArray1D(cctkGH, -1, handle, &local_array_in,
>>>> local_array_out, 4, CCTK_VARIABLE_REAL));
>>
>>
>> Thanks for the explanation.
>>
>> Actually what I have in my code is:
>>
>> 3)
>>
>> CCTK_REAL local_array_in,local_array_out;
>>
>> CCTK_INT handle = CCTK_ReductionArrayHandle("sum");
>>
>>
>> CCTK_ReduceLocArrayToArray1D(cctkGH, -1, handle, &local_array_in,
>> local_array_out, 4, CCTK_VARIABLE_REAL));
>>
>>
>> Is this correct? If I change the handle call to
>> CCTK_LocalArrayReductionHandle, I get this error at run time:
>>
>>
>> WARNING level 1 in thorn Cactus processor 0 host mbaiotti2.local
>>    (line 1120 of /Users/baiotti/Cactus/src/comm/Reduction.c):
>>    -> CCTK_LocalArrayReductionHandle: No handle: '-2' found for reduction
>> operator 'sum'
>>
>>
>> Luca
>
>
>