设计MPI程序模拟广播（MPI_Bcast）操作：将每个MPI进程按照所在节点名称建立node通信子域分组；再将各个node子通信域的0号进程再次组成一个名为head的通信域；在进行广播时，首先，由root进程将消息在head通信子域内广播，然后，再由head子域内各进程在其所在的node子域内进行广播。(Design the MPI program MPI_Bcast operation: Each MPI process establishes a node communication sub-domain grouping according to the node name; then, each process of the 0 node of each node sub-communication domain is again formed into a communication domain named head; At first, the root process broadcasts the message in the head communication sub-domain, and then the processes in the head sub-domain broadcast in the node sub-domain where it is)