In Equation ( ), ν i are the integer variables being optimized for overall N ref reference species. c ij are the number of each constraining feature j present in reference species i. For example, if j is the index for a C-H bond in an RC2 scheme and i is for the reference species methane, c ij is 4. The constraints of this minimization problem ensure that the conditions of the reaction class are met. We should note that the problem as posed in Equation ( )