Lambda Draw

λambda draw protocol

Diagrams for three destinations: live session files, vault course notes, and Anki cards. The failure mode this skill exists to kill: TikZ written blind and shipped unverified. You have vision — every figure gets rendered and looked at before it is embedded, no exceptions.

Medium decision table

Quantitative charts (a chart is a claim — the trap that shipped a wrong graph)

A wrong chart is a wrong claim delivered with false confidence. On surfaces where you cannot compile-and-LOOK (mermaid in chat, the lounge), the LOOK step becomes a trace-every-point check you run in your head before emitting.

mermaid xychart-beta — all binding:

• x-axis category labels MUST be unique. The band axis keys on the label string: two identical labels collapse to ONE slot, and any later point carrying that label jumps backward onto the earlier slot. This is the exact bug that shipped — an implied-vol series with x-axis ["pre-Q3","Q3 print","post","pre-Q4","Q4 print","post"] rendered its final point regressed, because the second "post" collapsed onto the first. For repeating phases, disambiguate: post-Q3, post-Q4.
• Data length == x-axis count. line [...] / bar [...] with N values needs exactly N x-categories, in the same order.
• y-axis range spans the data: y-axis "label" MIN --> MAX, MIN below the smallest value, MAX above the largest — else points clip at the frame.
• Trace every point before shipping. Read each value against its (unique) x-label and confirm the shape is what you meant: the monotone part is monotone, the sawtooth actually saws, the last point sits at the last x. This is the data-chart equivalent of the TikZ LOOK.

Prefer a labelled ASCII/Unicode plot for a quick trend, ≤ ~8 points, or when xychart fights you: it renders everywhere (monospace code fence), cannot collapse labels, and matches the house classical-print style. Hand-place the marks against a labelled axis and trace them the same way, e.g.:

implied vol (pts)
 58 ┤ ●
    │  \        ● rebuild is slow…
 42 ┤   ●______/ \
 38 ┤    \    /   \
 37 ┤     \__/     ●   ← still below, mean-reverting up into the next print
    └────┬────┬────┬────┬────┬────
      pre-Q3  post   Q4  post-Q4

Renderer note: LambdaMind's chat and session panes render mermaid natively (```mermaid fences). xychart-beta works there; the band-axis label-collapse is a mermaid property, not an app bug — uniqueness is on you. Never emit a chart you have not traced.

The TikZ loop (mandatory)

1. Write the picture into the scratchpad using the standalone harness from ~/lattice/org-notes/uni/Anki.md (binding — read it first in any session that draws for Anki):

   \documentclass[tikz,border=3pt]{standalone}
   \usepackage{amsmath,amssymb}
   \usetikzlibrary{arrows.meta,positioning,calc,backgrounds,shapes.geometric,fit}
   \begin{document}
   ...
   \end{document}
   

2. lualatex -interaction=nonstopmode -halt-on-error in the scratchpad.
3. pdftoppm -png -r 150 the result.
4. Read the PNG and inspect it: arrowheads point the right way; no label/edge collisions; observed nodes actually shaded; slices aligned; nothing orphaned or overlapping. Fix and recompile.
5. Budget ≤3 compile-view cycles; if it still fights you, simplify the figure (fewer nodes, drop the plate, straight edges) rather than fight TikZ. A clean simple figure beats a mangled ambitious one.
6. Only a viewed, passing figure may be embedded or pushed to a card.

PGM drawing conventions

• Latent variables: \node[vertex] (X1) {$X_1$}; with vertex/.style={circle, draw, minimum size=8mm}.
• Observed variables: observed/.style={vertex, fill=gray!30}.
• DBN/HMM time slices: one column per slice, transition arrows horizontal, emission arrows vertical, trailing \node {$\cdots$} for unrolling. 2-TBN form: two slices + the inter-slice arrows only.
• Plates: backgrounds layer + fit, label bottom-right.
• Undirected (Markov networks): plain -- edges, no arrowheads.
• Style names: never bare English words TikZ may own (out, in, at, to, node, edge, every, cap have all bitten). Use vertex, observed, slice, blanket.
• No pgfplots; hand-draw curves if ever needed.
• Course-faithful notation (check the course's own slides for symbol conventions before labelling).

Slide excerpts (fourth tier — not drawing, extracting)

When a teaching step cites slide/page $N$ of a course PDF, show it:

1. pdftoppm -png -r 150 -f N -l N <pdf> <scratchpad>/slide (single page).
2. If only a region matters, crop: magick <png> -crop WxH+X+Y +repage out.png — then view the result to confirm the crop caught the right region.
3. Copy to <vault>/sessions/assets/<lecture>-s<N>.png, embed relatively in the session file next to the teaching step.

Course slides are copyrighted: excerpts live in the private vault only — never in anything public, never in the OSS repo, never in shared decks.

Destinations

• Vault embed: save PNG to <vault>/courses/<course>/figs/<name>.png and embed relatively (![...](../courses/<course>/figs/<name>.png) from a session file, or wiki-embed). Keep the .tex source next to it.
• Anki card: the card carries the bare \begin{tikzpicture}... source (never wrapped in \[...\]) — only after the local compile passed. All Anki.md TikZ rules binding.
• Session file quick-structure: mermaid inline; no files.

Compile hygiene

All compiles run in the scratchpad, never in the vault. Copy in only the final PNG + tex source. If the vault is a git repo, figures ride the session's end-of-session commit.