Today it was bugging me that there is no tritosquare, to provide another way to make a lower-triangular matrix. Now there is, on git master and soonish to be released:

pdl> p ones(10)->tritosquare

[
 [1 0 0 0]
 [1 1 0 0]
 [1 1 1 0]
 [1 1 1 1]
]
[download]