[MPICH] about MPI_Reduce

[llwaeva at 21cn.com]

Hi there, 
  I use LAM/MPI under Linux and change to MPICH now. A similar question
about MPI_Reduce has been asked in the forum of LAM/MPI months ago. I
get some information from that reply but still have a question about that. I am 
wondering if there is any way to reduce a data of a special datatype(like 
checkboard-shape, with data located on the black grid) 

  It is easy to create such datatype(says CSData), however, the following 
calling is invalid in MPI as mentioned before 

MPI_Reduce( &src, &dest, 1, CSData, myOp, 0, MPI_COMM_WORLD); 

MPI_Reduce knows nothing about the CSData and only ONE element will be 
reduced actually. 

I am going to reduce the data limited by CSData. For that, I will first 
copy all data needed into a temporary buffer and then reduce the buffer, at 
last copy the buffer to the destionation accordingly to the checkboard 
structure. This method is too raw and the inefficient. I am looking for a 
better way!