LaTeX parsing: Error when parsing subscripts with multiple non-numeric symbols #255
Description
Description
I found a bunch of edge cases for parsing LaTeX expressions, specifically when dealing with variables that have multiple non-numeric symbols in their subscript. They either yield inconsistent results with expected cases or raise a MathJSON "incompaticle type" parsing error. This was tested on the mathlive.io demo website as of 10-10-2025.
Steps to Reproduce
import { ComputeEngine } from "@cortex-js/compute-engine"; const ce = new ComputeEngine(); const BATCH_1 = [ 'A_1', 'A_1+1', '2A_1', '2\\cdot A_1', '\\frac{A_1}{4}', 'A_1^2', ]; const BATCH_2 = [ 'A_{B}', 'A_{B}+1', '2A_{B}', '2\\cdot A_{B}', '\\frac{A_{B}}{4}', 'A_{B}^2', ]; const BATCH_3 = [ 'A_{CD}', 'A_{CD}+1', '2A_{CD}', '2\\cdot A_{CD}', '\\frac{A_{CD}}{4}', 'A_{CD}^2', ]; const BATCH_4 = [ 'AB_{CD}', 'AB_{CD}+1', '2AB_{CD}', '2\\cdot AB_{CD}', '\\frac{AB_{CD}}{4}', 'AB_{CD}^2', ]; function convertLatexToMathJson(latex) { const parsedExpr = ce.parse(latex); const boxedExpr = ce.box(parsedExpr, { canonical: true }); return boxedExpr.json; } // Run testing console.log('Batch 1 Testing'); for (const expr of BATCH_1) { const mjson = convertLatexToMathJson(expr); console.log(expr, ' => ', JSON.stringify(mjson, null, 2)); } console.log(); console.log('Batch 2 Testing'); for (const expr of BATCH_2) { const mjson = convertLatexToMathJson(expr); console.log(expr, ' => ', JSON.stringify(mjson, null, 2)); } console.log(); console.log('Batch 3 Testing'); for (const expr of BATCH_3) { const mjson = convertLatexToMathJson(expr); console.log(expr, ' => ', JSON.stringify(mjson, null, 2)); } console.log(); console.log('Batch 4 Testing'); for (const expr of BATCH_4) { const mjson = convertLatexToMathJson(expr); console.log(expr, ' => ', JSON.stringify(mjson, null, 2)); }Raw Script Output
Batch 1 Testing (Working)
A_1 => "A_1" A_1+1 => [ "Add", "A_1", 1 ] 2A_1 => [ "Multiply", 2, "A_1" ] 2\cdot A_1 => [ "Multiply", 2, "A_1" ] \frac{A_1}{4} => [ "Multiply", [ "Rational", 1, 4 ], "A_1" ] A_1^2 => [ "Power", "A_1", 2 ] Batch 2 Testing (Working)
A_{B} => "A_B" A_{B}+1 => [ "Add", "A_B", 1 ] 2A_{B} => [ "Multiply", 2, "A_B" ] 2\cdot A_{B} => [ "Multiply", 2, "A_B" ] \frac{A_{B}}{4} => [ "Multiply", [ "Rational", 1, 4 ], "A_B" ] A_{B}^2 => [ "Power", "A_B", 2 ] Batch 3 Testing
A_{CD} => [ "Subscript", "A", [ "InvisibleOperator", "C", "D" ] ] A_{CD}+1 => [ "Add", [ "Error", [ "ErrorCode", "'incompatible-type'", "number", "symbol" ] ], 1 ] 2A_{CD} => [ "Tuple", 2, [ "Subscript", "A", [ "InvisibleOperator", "C", "D" ] ] ] 2\cdot A_{CD} => [ "Multiply", 2, [ "Error", [ "ErrorCode", "'incompatible-type'", "number", "symbol" ] ] ] \frac{A_{CD}}{4} => [ "Divide", [ "Error", [ "ErrorCode", "'incompatible-type'", "number", "symbol" ] ], 4 ] A_{CD}^2 => [ "Power", [ "Error", [ "ErrorCode", "'incompatible-type'", "number", "symbol" ] ], 2 ] Batch 4 Testing
AB_{CD} => [ "Tuple", "A", [ "Subscript", "B", [ "InvisibleOperator", "C", "D" ] ] ] AB_{CD}+1 => [ "Add", [ "Error", [ "ErrorCode", "'incompatible-type'", "number", "'tuple<unknown, symbol>'" ] ], 1 ] 2AB_{CD} => [ "Tuple", 2, "A", [ "Subscript", "B", [ "InvisibleOperator", "C", "D" ] ] ] 2\cdot AB_{CD} => [ "Multiply", 2, [ "Error", [ "ErrorCode", "'incompatible-type'", "number", "'tuple<unknown, symbol>'" ] ] ] \frac{AB_{CD}}{4} => [ "Divide", [ "Error", [ "ErrorCode", "'incompatible-type'", "number", "'tuple<unknown, symbol>'" ] ], 4 ] AB_{CD}^2 => [ "Tuple", "A", [ "Power", [ "Error", [ "ErrorCode", "'incompatible-type'", "number", "symbol" ] ], 2 ] ] Environment
Screenshots are from mathlive.io demo website: https://mathlive.io/mathfield/demo/ using compute engine v0.30.2.
Testing code is ran against Node.js v22.20.0 and NPM v10.9.3 using compute engine v0.30.2.