> pss("diagonal", nrow = 7, ncol = 9)
/ - - - - - - - - - \ 
| 1 2 3 1 2 3 1 2 3 | 
| 3 1 2 3 1 2 3 1 2 | 
| 2 3 1 2 3 1 2 3 1 | 
| 1 2 3 1 2 3 1 2 3 | 
| 3 1 2 3 1 2 3 1 2 | 
| 2 3 1 2 3 1 2 3 1 | 
| 1 2 3 1 2 3 1 2 3 | 
\ - - - - - - - - - /