Generate the stoichiometry (|u| by |v|) matrix for the SPN.
Each column gives the net effect of that transition firing upon the state
space of the model. Internally, this creates a Pre (spn_Pre) and
Post (spn_Post) matrix, and then calculates the final stoichiometry.
Details
The places (spn_P) object is generated from one of the following:
spn_P_lifecycle_node, spn_P_lifecycle_network,
spn_P_epiSIS_node, spn_P_epiSIS_network,
spn_P_epiSEIR_node, or spn_P_epiSEIR_network.
The set of transitions (spn_T) is generated from one of the following:
spn_T_lifecycle_node, spn_T_lifecycle_network,
spn_T_epiSIS_node, spn_T_epiSIS_network,
spn_T_epiSEIR_node, spn_T_epiSEIR_network.