Gather/Scatter

• Suppose we want to perform a parallel matrix-vector product

• Start with sequential dot product based algorithm for y=Ax

void Serial_matrix_vector_prod(

MATRIX_T A /* in mxn*/,

int m /* in */,

int n /* in */,

float x[] /* in n-vec*/,

float y[] /* out m-vec*/) {

int k, j;

for (k = 0; k < m; k++) {

y[k] = 0.0;

for (j = 0; j < n; j++)

y[k] = y[k] + A[k][j]*x[j];

}

} /* Serial_matrix_vector_prod */

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