c - how to parallelize a dot product with MPI -

i've been trying learn mpi , i've code snippet c should formatted mpi make parallizable;

// dot product int a[100000]; int b[100000]; int c=0;  (int i=0 ; i<100000; i++){     c += a[i] * b[i]; } 

im kinda confused of how deal for-loops when using mpi answer exercise;

// dot product int a[100000]; int b[100000]; int c=0; int rootid = 0; int  numtasks, taskid, len, partner, message; mpi_status status; mpi_init(&argc, &argv); mpi_comm_rank(mpi_comm_world, &taskid);      (int i=0 ; i<100000; i++){     c = a[i] * b[i];      if(rootid == taskid){         mpi_send(&a[100000], &b[100000], mpi_int, 1, 0, mpp_comm_world, mpi_status)      }else if (rootid < taskid){         mpi_recv(c, 100000, mpi_int, 0, 0, mpp_comm_world, mpi_status)     }      mpi_finalize(); return 0;  } 

im not sure if correct, believe im in right direction...

the problem mpi can't find examples of how rewrite or structe loops - there examples in fortran nothing im familiar with... i've seen simple examples of "hello world" c in mpi.... nothing useful there.

all appreciated..

was there typo , did mean instead ?

for (int i=0 ; i<100000; i++){     c += a[i] * b[i]; } 

parallelization heavily depends on how arrays a , b distributed.

the simplest case, 1 biggest memory footprint, have full arrays a , b on mpi tasks. based on task rank , total number of tasks, each task can compute part of dot product e.g.

for (int i=start; i<end; i++) {     c += a[i] * b[i]; } 

and can mpi_reduce()/mpi_allreduce() mpi_sum partial dot products in order final result.