The problem is minloc and maxloc need to go away. better to use a custom op. 

> On Aug 10, 2018, at 9:36 AM, George Bosilca <bosi...@icl.utk.edu> wrote:
> 
> You will need to create a special variable that holds 2 entries, one for the 
> max operation (with whatever type you need) and an int for the rank of the 
> process. The MAXLOC is described on the OMPI man page [1] and you can find an 
> example on how to use it on the MPI Forum [2].
> 
> George.
> 
> 
> [1] https://www.open-mpi.org/doc/v2.0/man3/MPI_Reduce.3.php
> [2] https://www.mpi-forum.org/docs/mpi-1.1/mpi-11-html/node79.html
> 
>> On Fri, Aug 10, 2018 at 11:25 AM Diego Avesani <diego.aves...@gmail.com> 
>> wrote:
>>  Dear all,
>> I have probably understood.
>> The trick is to use a real vector and to memorize also the rank.
>> 
>> Have I understood correctly?
>> thanks
>> 
>> Diego
>> 
>> 
>>> On 10 August 2018 at 17:19, Diego Avesani <diego.aves...@gmail.com> wrote:
>>> Deal all,
>>> I do not understand how MPI_MINLOC works. it seem locate the maximum in a 
>>> vector and not the CPU to which the valur belongs to.
>>> 
>>> @ray: and if two has the same value?
>>> 
>>> thanks 
>>> 
>>> 
>>> Diego
>>> 
>>> 
>>>> On 10 August 2018 at 17:03, Ray Sheppard <rshep...@iu.edu> wrote:
>>>> As a dumb scientist, I would just bcast the value I get back to the group 
>>>> and ask whoever owns it to kindly reply back with its rank.
>>>>      Ray
>>>> 
>>>> 
>>>>> On 8/10/2018 10:49 AM, Reuti wrote:
>>>>> Hi,
>>>>> 
>>>>>> Am 10.08.2018 um 16:39 schrieb Diego Avesani <diego.aves...@gmail.com>:
>>>>>> 
>>>>>> Dear all,
>>>>>> 
>>>>>> I have a problem:
>>>>>> In my parallel program each CPU compute a value, let's say eff.
>>>>>> 
>>>>>> First of all, I would like to know the maximum value. This for me is 
>>>>>> quite simple,
>>>>>> I apply the following:
>>>>>> 
>>>>>> CALL MPI_ALLREDUCE(eff, effmaxWorld, 1, MPI_DOUBLE_PRECISION, MPI_MAX, 
>>>>>> MPI_MASTER_COMM, MPIworld%iErr)
>>>>> Would MPI_MAXLOC be sufficient?
>>>>> 
>>>>> -- Reuti
>>>>> 
>>>>> 
>>>>>> However, I would like also to know to which CPU that value belongs. Is 
>>>>>> it possible?
>>>>>> 
>>>>>> I have set-up a strange procedure but it works only when all the CPUs 
>>>>>> has different values but fails when two of then has the same eff value.
>>>>>> 
>>>>>> Is there any intrinsic MPI procedure?
>>>>>> in anternative,
>>>>>> do you have some idea?
>>>>>> 
>>>>>> really, really thanks.
>>>>>> Diego
>>>>>> 
>>>>>> 
>>>>>> Diego
>>>>>> 
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