You are right. It is buf + i*extent, not lower_bound + i*extent. This stuff is confusing. Right now, I am not coming up with a good example of where a non-zero lower bound makes a difference. Rajeev

On Dec 9, 2016, at 9:31 AM, [email protected] <[email protected]> wrote:

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, [email protected] <[email protected]> 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

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