josdejong/mathjs

Better documentation of usolve limitations, or possibly error message when input is not upper triangular?

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#2,333 opened on Oct 6, 2021

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 (4 comments) (0 reactions) (0 assignees)JavaScript (13,832 stars) (1,298 forks)batch import
documentationfeaturehelp wanted

Description

Minimal code:

window.onload = function() {
	const U = math.matrix([[0.10452846326765346,-120],[-0.9945218953682733,-0]])
	const b = math.matrix([-22.163070207475485, -59.419761706007094])

	result = math.usolve(U,b)
	console.log(result)	
}

The error I get: Uncaught Error: Linear system cannot be solved since matrix is singular.

I entered the very same equation into GNU Octave which was able to solve it: it is no unsolvable system. When switching the lines, it even becomes an upper triangular matrix with nonzero values on the diagonal line. So its determinant is not zero, which implicates that the matrix is not even singular!

Contributor guide

Tech stack
javascript
Domain
documentation
Issue type
documentation
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
under 1 hour
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
basic linear algebrafamiliarity with mathjs usolve
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
70
Research direction
The issue requests better documentation or error message when the input matrix to usolve is not upper triangular. Investigate the usolve implementation in src/function/algebra/solver/usolve.js to add a check for non upper triangular input and provide a descriptive error message. Update the documentation in the usolve function's JSDoc or the library's documentation site to clearly state that the input must be upper triangular. The issue comments confirm the need for clarity.