Hi over there, this blog muses about an exercise (May, 2012) at the Ponder This site of IBM Research.

The pages show examples for different row numbers Z, starting with the minimum Z = 2 but aiming for preferably big row numbers, whereas the posts consider issues with the example generation.

Take time and step in a matrix from one partial sum to the next. For small matrices this is obvious and rather trivial, for the bigger ones it needs quite an amount of memory, even if the partial sums are indicated.