for each (S i , S k ) connected pair in the SMARTS hierarchy where α is the required absolute difference induced by the split, and µ k and µ i are the means of the data matched to the respective pair of (S k , S i ) SMARTS patterns. Similar to the categorical case, we require that all X split < 0 and the total objective (Eqn. 18) decreases in order to accept a new SMARTS into the hierarchy. Additionally analogous to the categorical case, the set of SMARTS {S k } SMARTS are pruned where X split ≥ 0.