# Multiplicity

Multiplicity defines the number of reaction paths from reactants to products. If there is only one reaction path from reactants to products, the multiplicity is 1. If there are multiple, indistinguishable reaction paths, multiplicity is greater than 1. Multiplicity directly depends on reaction symmetry and can differ for reactions within the same reaction class.

In the process of network generation, the multiplicity of a reaction has an initial value of 1 and is then incremented as indistinguishable instances of the reaction are generated. Reaction rates and multiplicity are directly implicated in the overall effective rate constant of a reaction. In particular, an effective rate constant is the product of the rate constant as specified in the matching reaction rule and the multiplicity of the reaction.