Figure 4
From: Efficient edit distance with duplications and contractions
The tree of recursive calls to COMPUTE-MATRIX. Each call over a region containing more than one entry partitions the region either vertically or horizontally, and performs two recursive calls over the two sub-regions. After the first call was performed (the left or top sub-region for vertical or horizontal partition, respectively), a matrix multiplication involving the computed region is computed in order to meet the precondition required for the computation of the sibling region.