How would you implement a huge-but-sparse 2D matrix in Erlang?

• First solution who came to my mind was to google for some linear algebra library ... that failed!
• The second one, implement a dict-of-dict structure.

That was quite easy, but as I was wondering on efficiency I needed to understand differences between dict, orddict etc. On my way I came up with this (ongoing) list of Erlang data structures.