[Users] CCTK_ReductionArrayHandle

[Erik Schnetter]

The new API requires LocalReduce.

PUGH uses the new API, Carpet uses the old API.

LocalReduce has bugs, e.g. for complex numbers, and possible for some norms.

-erik

On Fri, Aug 3, 2012 at 7:49 AM, Luca Baiotti <baiotti at ile.osaka-u.ac.jp> wrote:
> 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
>>
>>
>>
>>
>



-- 
Erik Schnetter <schnetter at cct.lsu.edu>
http://www.perimeterinstitute.ca/personal/eschnetter/