[Mpi-forum] Interest of changing lower bound in MPI_Type_create_resized

[lecas@idris.fr]

Le 12/08/2016 à 03:14 PM, Thakur, Rajeev a écrit :
> When MPI sends a message, the second datatype is taken from the location (lower bound + extent), the third datatype from (lower bound + 2*extent), and so on. So the lower bound does affect what is sent.
>
> Rajeev
>

This is not what i understand from the chapter 4.1.11 Use of General
Datatypes in Communication

If a datatype have n entries and we are sending count datatype

i=0,..., count-1
j=0,..,n-1

So the address in memory to get each entries is : addr(i,j) =
buf+extent*i+disp(j)

There is nowhere the usage of lower bound for having location of next
datatype.
buf is the argument in send/recv function.



>> On Dec 8, 2016, at 7:54 AM, lecas at idris.fr <dimitri.lecas at idris.fr> wrote:
>>
>> Hi,
>>
>> In MPI_Type_create_resized we can change the extent  and the lower bound.
>>
>> I don't understand what is the interest of changing the lower bound,
>> since for sending message, only the extent is used.
>>
>> Is  there an example where the value for lower bound in
>> MPI_Type_create_resized have a real impact ?
>>
>> Thanks
>>
>> -- 
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> Dimitri Lecas
>>
>>
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-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Dimitri Lecas
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


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