Module point_figure 

Point & Figure column construction (close-based, N-box reversal).

A Point & Figure chart discards time and volume and reduces price to a grid of boxes of height box_size. Price movement is drawn as columns: rising columns of X’s and falling columns of O’s. A column keeps extending while price advances by whole boxes, and a new (opposite) column starts only when price reverses by at least reversal boxes from the current column’s extreme — the classic N-box reversal filter (reversal = 3 is the traditional default).

This implements the close-price construction: each bar contributes its close, quantised to the box grid floor(price / box_size). On a reversal the new column begins one box back from the prior extreme (the standard top − 1 … top − N placement).

Sources:

• Cohen, A. W. (1947), How to Use the Three-Point Reversal Method of Point & Figure Stock Market Trading — origin of the three-box (N-box) reversal.
• du Plessis, J. (2012), The Definitive Guide to Point and Figure, 2nd ed. — modern box-size / reversal construction; the close-price method.

Two surfaces kept in parity (see the proptest):

• streaming: PointFigureBuilder::next pushes one close, returns a completed column when a reversal starts a new one (else None);
• batch: point_figure_batch folds the builder over a close slice.

Structs

PointFigureBuilder

Stateful close-based Point & Figure builder.

PointFigureColumn

One completed Point & Figure column. direction is +1 (X, rising) or -1 (O, falling); top/bottom are the column’s high/low box levels (top >= bottom); boxes is the span between them in box_size units.

Functions

point_figure_atr_batch

ATR-box Point & Figure: box size is multiplier * atr (a single representative ATR), matching the ATR-box convention of the other bar types.

point_figure_batch

Batch Point & Figure: fold PointFigureBuilder over a close slice.