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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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

Research direction
Investigate why usolve considers the given matrix singular. Test if the matrix is actually upper triangular; check for numerical precision issues. Consider improving the error message or documentation to clarify the solver's limitations (e.g., requirement for non singular upper triangular matrix).
Tech stack
javascript
Domain
api
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
JavaScriptlinear algebra
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
65