A linear-programming problem in which the constraint set can be arranged into connecting blocks such that the first block is connected to the second block by a few variables, the second block is connected to the third block by a few variables, and so on. Staircase structures arise in production problems over time in which the connecting variables are inventories that carry over from one time period to the next. The matrix of coefficients defined by such structures is very sparse. Block angular systems; Large-scale systems; Super sparsity; Weakly-coupled systems.