Figure 2
From: Systematic benchmark of substructure search in molecular graphs - From Ullmann to VF2
Iteration of Ullmann algorithm. One step of the Ullmann algorithm. The initial compatibility matrix (left) shows carboxylic acid substructure nodes as rows and heptonic acid molecule atoms as columns. A non-zero entry indicates the compatibility of a node-atom pair. Zero entries are not shown. In the current row, indicated in gray, the algorithm choses one compatible node-atom mapping (middle) and refines all unprocessed rows (right). The algorithm continues with the next row. Figure 3 illustrates the refinement.