tree structure, signed area, generating simple Sudoku N^2, all integer partition, paging with SSD, D3 for web graphics, present documents in print and on web

Location
Heartland

## Agenda

```             Meeting Agenda for NYCJUG 20121113
----------------------------------
1. Beginner's regatta: some ideas for working with trees in J: see
"PlantingTrees.doc".

Calculating signed area in two dimensions: see "SimpleSignedAreaExamples.doc".

2. Show-and-tell: a little more Sudoku: see "Researchers make Sudoku puzzles
less puzzling.doc" and "SimpleGeneralSudokuGeneration.doc".

Testing "all-integer partitions" J code: see "Paging Performance Penalty When
Using an SSD.doc".

3. Advanced topics: better web graphics in J: see "D3 for J - intro.doc".

4. Learning, teaching and promoting J, et al.: presenting complex documents in
print and on the web: see "Routing Between Different Display Formats.doc".

Another J package we could use: see "Factor Analysis Question.doc".```

## Beginner's Regatta

There has been discussion on the forum recently of how to represent a tree data structure in J. This is a question that recurs, albeit infrequently, and there is at least one time-honored solution to this dating back to APL days. In brief, the tree structure is represented by a vector of integers of the index of the parent of each node, with _1 for a root node. This is explained more fully on this page.

A different question that comes up rarely, if ever, is how to calculate a signed area. However, this is an interesting idea with some intriguing potential uses, but is only explained briefly here. The concept seemed to be worth further elaboration, as is done here.