There are several system calls that provide information about a hypercube or a node.
Associated with each node of a hypercube is a logical node number which ranges from 0 to n-1 where n is the number of nodes in the hypercube. mynode() returns the number of the node on which the calling process is executing. numnodes() returns the number of nodes in the current hypercube and nodedim() returns the dimension of the current hypercube.
In many of the system calls, a node number, a pid or a message type have to be specified. -1 is the wild card for system calls. It can be used to specify all the nodes, all the processes, or all message types.