xbt_matrix_t sM;
for(node=0; node < num_nodes; node++){
snprintf(node_mbox, MAILBOX_NAME_SIZE - 1, "%d", nodes[node]);
sM = xbt_matrix_new_sub(M, NODE_MATRIX_SIZE, NODE_MATRIX_SIZE, 0, 0, NULL);
task = MSG_task_create("sub-matrix", 100, 100, sM);
xbt_matrix_t sM;
for(node=0; node < num_nodes; node++){
snprintf(node_mbox, MAILBOX_NAME_SIZE - 1, "%d", nodes[node]);
sM = xbt_matrix_new_sub(M, NODE_MATRIX_SIZE, NODE_MATRIX_SIZE, 0, 0, NULL);
task = MSG_task_create("sub-matrix", 100, 100, sM);