Parallel read of a nxn matrix stored in a file -

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i'm developing program, solve equation ax = b using gaussian elimination. i've got file, in i've stored matrix of type double (row major order since using c). i'm trying read file in parallel, using parallel file i/o functions provided mpi.

i've gained understanding of mpi_file_set_view , how logically partitions shared file each process has different view of file. i've understood view must consist of etype, filetype , displacement. in case, i've got have cyclic row distribution , i've got following code: 

int count, blksize, stride,lb,extent;     mpi_file fh;     mpi_offset of;     /* define types etype, ftype       etype: type of data stored in file.        ftype: description of how data stored in file.        */     mpi_datatype etype, ftype,mpi_vect;     /* etype:       */     count = (n + (size -1))/size; blksize = n;     stride = size;     lb = 0; extent = n*sizeof(double);     mpi_type_vector(count,blksize,stride,mpi_double,&mpi_vect);     mpi_type_create_resized(mpi_vect,lb,extent,&etype);     mpi_type_commit(&etype);          /* ftype: describes logical division of file.       strided vector of blocksize 1 , count n/size.       stride size     */      mpi_type_vector(count,1,stride, mpi_double, &ftype);      mpi_type_commit(&ftype);     mpi_file_open(mpi_comm_world,filename,mpi_mode_rdonly,mpi_info_null,&fh);     mpi_file_set_view(fh,0,etype,ftype,native,mpi_info_null);     /* assume buf allocated mpi_vector blocksize equal row size , stride equal number of processors */     mpi_file_read(fh,buf,count,mpi_vec,mpi_status_ignore);

my question is, how decide proper etype , ftype? appreciated.

thanks.

etype , ftype still trip me , i've been working mpi-io 15 years. concept isn't tough, reason naming convention not stick me.

the etype or "elementary type" sets fundamental unit various counts. when call mpi_file_read_at_all , give offset, offset count of etype. not bytes.

there 2 ways read particular region of file: can adjust file view on each process start want, or can use explicit offset routines (e.g. mpi_file_read_at_all). if constructing file view each process might not need worry etype: set mpi_byte.


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