[AbsoluteValue] PR4 - scoring

[handeyeco]

Everything is AI

Summary:

This is part of a series of PRs as defined in the first PR:

• Perseus#3346: PR implementation guide
• Perseus#3348: PR1 - type definitions and schema
• Perseus#3349: PR2 - state management
• Perseus#3350: PR3 - rendering & accessibility
• ▶️ Perseus#3351: PR4 - scoring
• Perseus#3352: PR5 - editor support
• Perseus#3380: Convert todo into a long-term doc

Initial implementation experiment is Perseus#3304.

Issue: LEMS-3347

---

Add scoring for absolute-value graph type

Implements scoring for the absolute-value graph, isolated from rendering.
Depends on PR 1 for the type definitions. Can be developed in parallel with
PR 3.

Changes:

• kmath/src/coefficients.ts — Adds getAbsoluteValueCoefficients(coords), a
  canonical coefficient extractor returning [m, h, v] as an
  AbsoluteValueCoefficient tuple (or undefined if the two points share the
  same x). Lives in kmath alongside getSinusoidCoefficients and
  getQuadraticCoefficients for reuse by the scorer without taking a
  dependency on the rendering package.
• kmath/src/index.ts — Exports the new AbsoluteValueCoefficient type.
• data-schema.ts — Adds AbsoluteValueGraphCorrect (type: "absolute-value",
  coords: [Coord, Coord]) and includes it in the PerseusGraphCorrectType
  union, which is required for the rubric type to accept absolute-value
  correct answers.
• score-interactive-graph.ts — Adds an else if branch for "absolute-value":
  extracts [m, h, v] coefficients from both the user input and rubric
  coords, then uses approximateDeepEqual to compare them. No canonical
  normalization is needed — the vertex uniquely defines position and m
  uniquely defines shape and orientation.
• score-interactive-graph.test.ts — Six tests covering: undefined guess
  (invalid), missing coords (invalid), wrong slope (incorrect), correct
  answer, symmetry (p2 on either arm of the same V scores correctly), and
  downward-opening vs upward-opening mismatch (incorrect).

[github-actions]

🗄️ Schema Change: Changes Detected ⚠️

Usually this means you need to update the Go parser
that Content Platform maintains!!!
See this list of post-mortems for more information.

This PR contains critical changes to Perseus. Please review
the changes and note that you may need to coordinate
deployment of these changes with other teams at Khan Academy.

diff --unified /home/runner/work/_temp/branch-compare/base/schema.d.ts /home/runner/work/_temp/branch-compare/pr/schema.d.ts
--- /home/runner/work/_temp/branch-compare/base/schema.d.ts	2026-03-23 20:38:21.122849324 +0000
+++ /home/runner/work/_temp/branch-compare/pr/schema.d.ts	2026-03-23 20:38:08.655547806 +0000
@@ -728,6 +728,10 @@
     coords?: CollinearTuple | null;
     startCoords?: CollinearTuple;
   };
+  type AbsoluteValueGraphCorrect = {
+    type: "absolute-value";
+    coords: [Coord, Coord];
+  };
   type AngleGraphCorrect = {
     type: "angle";
     allowReflexAngles: boolean;
@@ -780,6 +784,7 @@
     coords: CollinearTuple;
   };
   export type PerseusGraphCorrectType =
+    | AbsoluteValueGraphCorrect
     | AngleGraphCorrect
     | CircleGraphCorrect
     | LinearGraphCorrect

[github-actions]

🛠️ Item Splitting: No Changes ✅

[github-actions]

Size Change: +113 B (+0.02%)

Total Size: 490 kB

Filename	Size	Change
packages/kmath/dist/es/index.js	6.08 kB	+56 B (+0.93%)
packages/perseus-score/dist/es/index.js	9.5 kB	+57 B (+0.6%)

ℹ️ View Unchanged

Filename	Size
packages/kas/dist/es/index.js	20.5 kB
packages/keypad-context/dist/es/index.js	1 kB
packages/math-input/dist/es/index.js	98.5 kB
packages/math-input/dist/es/strings.js	1.61 kB
packages/perseus-core/dist/es/index.item-splitting.js	11.9 kB
packages/perseus-core/dist/es/index.js	25 kB
packages/perseus-editor/dist/es/index.js	100 kB
packages/perseus-linter/dist/es/index.js	8.82 kB
packages/perseus-utils/dist/es/index.js	403 B
packages/perseus/dist/es/index.js	190 kB
packages/perseus/dist/es/strings.js	7.84 kB
packages/pure-markdown/dist/es/index.js	1.39 kB
packages/simple-markdown/dist/es/index.js	6.71 kB

_{compressed-size-action}

[github-actions]

npm Snapshot: Published

Good news!! We've packaged up the latest commit from this PR (2c8e427) and published it to npm. You
can install it using the tag PR3351.

Example:

pnpm add @khanacademy/perseus@PR3351

If you are working in Khan Academy's frontend, you can run the below command.

./dev/tools/bump_perseus_version.ts -t PR3351

If you are working in Khan Academy's webapp, you can run the below command.

./dev/tools/bump_perseus_version.js -t PR3351

[claude]

LGTM — straightforward extension of existing graph scoring patterns to support absolute-value graphs.

Extended reasoning...

Overview

This PR adds absolute-value graph support to the interactive graph scoring system across 5 files: a new getAbsoluteValueCoefficients function in kmath, its type export, an AbsoluteValueGraphCorrect type in the data schema union, scoring logic in score-interactive-graph.ts, and comprehensive tests.

Security risks

None. This is pure math/scoring logic with no I/O, auth, or external interactions.

Level of scrutiny

Low scrutiny warranted. The changes mechanically follow the exact same pattern used for quadratic and sinusoid graph scoring. The coefficient computation is straightforward: Math.abs(rise/run) with sign determined by whether p2 is above or below the vertex, which correctly handles points on either arm of the V. The scoring branch mirrors the quadratic branch (compute coefficients, compare with approximateDeepEqual).

Other factors

• Good test coverage: 6 tests covering invalid input (undefined guess, missing coords), wrong answer, exact match, symmetry (point on other arm), and direction mismatch (upward vs downward).
• The new AbsoluteValueGraphCorrect type is correctly added to the PerseusGraphCorrectType union, which is the type used by PerseusInteractiveGraphRubric.correct.
• The PerseusGraphTypeAbsoluteValue type already existed in the data schema, so this PR just adds the scoring support.
• PR description is empty, but the code is self-explanatory given the established patterns.

[ivyolamit]

Changes looks logical to me 👍🏼