This method includes: obtaining first data including identifiers of selected computers for invocation of parallel processes among plural computers connected to lowest-layer relay apparatuses in a network including relay apparatuses in plural layers, wherein the network includes paths between a relay apparatus in a first layer and plural relay apparatuses in a second layer that is an immediately upper layer than the first layer; and selecting, for each of the selected computers and from network identifiers for respective communication routes, network identifiers to be used for communication with other selected computers so as to avoid coincidence of communication routes between the selected computers for which a same difference value is calculated between identification numbers, wherein the network identifiers are associated in advance with an identifier of each of the plural computers and are used for routing in the network, and the identification numbers are assigned for ordering the selected computers.