Eq[Polynomial[C]] throws ArrayIndexOutOfBoundsException for negative exponents

Description

scala> def x: Polynomial[Int] = PolySparse(List(Term(-1642198702, -1)))
x: spire.math.Polynomial[Int]
scala> x === x
java.lang.ArrayIndexOutOfBoundsException: -1
  at scala.runtime.ScalaRunTime$.array_update(ScalaRunTime.scala:76)
  at spire.math.poly.PolySparse.coeffsArray(PolySparse.scala:54)
  at spire.math.PolynomialEq.eqv(Polynomial.scala:556)
  at spire.math.PolynomialEq.eqv$(Polynomial.scala:555)
  at spire.math.PolynomialInstances0$$anon$14.eqv(Polynomial.scala:568)
  ... 36 elided

Contributor guide

Tech stack

scala

Domain

data

Issue type

bug

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

Scala basicsArray indexing

Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.

80

Research direction

Investigate the PolySparse.coeffsArray method at line 54 of PolySparse.scala. Determine why negative exponents cause an ArrayIndexOutOfBoundsException. Consider adding a validation or adjusting the method to handle negative exponents. Write a test case with a polynomial like PolySparse(List(Term( 1642198702, 1))) to verify the fix.