Never mind, Rajeev was right; I missed the medium messages with powers of two case. --Halim On 5/9/16 12:45 PM, Halim Amer wrote:

Looking at the code, for long messages the same ring algorithm is used for long/medium messages regardless of whether the number of processes is a power of two or not. The comment is wrong. We will fix it, but in general one shouldn't rely solely on code comments and should look at the code itself.

--Halim www.mcs.anl.gov/~aamer

On 5/9/16 12:21 PM, Jen B wrote:

...

Hello,

I am looking at allgatherv.c from:

git.mpich.org/mpich.git/tree/HEAD:/src/mpi/coll <http://git.mpich.org/mpich.git/tree/HEAD:/src/mpi/coll>

It says the following:

"For short or medium-size messages and power-of-two no. of processes, we use the recursive doubling algorithm. ... For long messages or medium-size messages and non-power-of-two no. of processes, we use a ring algorithm. ..."

Could someone please tell me what algorithm is used when we have "long messages and power-of-two no. of processes"? Thanks a lot!

Best, Jen

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