Dot Product Example

Assume that the data is block distributed (i.e. process 0 had the first n/p components of x and y, processor 1 the next n/p, etc.)

float local_x[] /* in */,

float local_y[] /* in */,

int n_bar /* in */) {

float local_dot;

float dot = 0.0;

float Serial_dot(float x[], float y[], int m);

local_dot = Serial_dot(local_x, local_y, n_bar);

MPI_Reduce(&local_dot, &dot, 1, MPI_FLOAT,

MPI_SUM, 0, MPI_COMM_WORLD);

return dot;

} /* Parallel_dot */

Assume that n is divisible by P