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Subject: Re: [OMPI users] MPI-Send for entire entire matrix when allocating memory dynamically
From: Natarajan CS (csnataraj_at_[hidden])
Date: 2009-10-29 14:30:22


Hi
   thanks for the quick response. Yes, that is what I meant. I thought there
was no other way around what I am doing but It is always good to ask a
expert rather than assume!

Cheers,

C.S.N

On Thu, Oct 29, 2009 at 11:25 AM, Eugene Loh <Eugene.Loh_at_[hidden]> wrote:

> Natarajan CS wrote:
>
> Hello all,
>> Firstly, My apologies for a duplicate post in LAM/MPI list I have
>> the following simple MPI code. I was wondering if there was a workaround for
>> sending a dynamically allocated 2-D matrix? Currently I can send the matrix
>> row-by-row, however, since rows are not contiguous I cannot send the entire
>> matrix at once. I realize one option is to change the malloc to act as one
>> contiguous block but can I keep the matrix definition as below and still
>> send the entire matrix in one go?
>>
>
> You mean with one standard MPI call? I don't think so.
>
> In MPI, there is a notion of derived datatypes, but I'm not convinced this
> is what you want. A derived datatype is basically a static template of data
> and holes in memory. E.g., 3 bytes, then skip 7 bytes, then another 2
> bytes, then skip 500 bytes, then 1 last byte. Something like that. Your 2d
> matrices differ in two respects. One is that the pattern in memory is
> different for each matrix you allocate. The other is that your matrix
> definition includes pointer information that won't be the same in every
> process's address space. I guess you could overcome the first problem by
> changing alloc_matrix() to some fixed pattern in memory for some r and c,
> but you'd still have pointer information in there that you couldn't blindly
> copy from one process address space to another.
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