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Posted to issues@commons.apache.org by "ASF GitHub Bot (Jira)" <ji...@apache.org> on 2021/07/19 14:17:00 UTC
[jira] [Work logged] (MATH-1617) FieldLUDecomposition with BigReal
throw divide by zero error
[ https://issues.apache.org/jira/browse/MATH-1617?focusedWorklogId=624378&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-624378 ]
ASF GitHub Bot logged work on MATH-1617:
----------------------------------------
Author: ASF GitHub Bot
Created on: 19/Jul/21 14:16
Start Date: 19/Jul/21 14:16
Worklog Time Spent: 10m
Work Description: samabcde opened a new pull request #192:
URL: https://github.com/apache/commons-math/pull/192
Related ticket: https://issues.apache.org/jira/browse/MATH-1617#
Previous provided fix on changing `BigReal#equals` but `hashcode` is not updated, providing inconsistent result.
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Issue Time Tracking
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Worklog Id: (was: 624378)
Remaining Estimate: 0h
Time Spent: 10m
> FieldLUDecomposition with BigReal throw divide by zero error
> ------------------------------------------------------------
>
> Key: MATH-1617
> URL: https://issues.apache.org/jira/browse/MATH-1617
> Project: Commons Math
> Issue Type: Bug
> Affects Versions: 3.6.1
> Reporter: Ng Tsz Sum
> Priority: Major
> Fix For: 4.0
>
> Attachments: MATH-1617.patch
>
> Time Spent: 10m
> Remaining Estimate: 0h
>
> From [https://stackoverflow.com/questions/68427448/how-to-find-the-inverse-of-a-matrix-using-apache-commons-math-library-in-java/68427869?noredirect=1#comment120932354_68427869]
> h3. Reproducible example
> {code:java}
> import org.apache.commons.math3.linear.FieldLUDecomposition;
> import org.apache.commons.math3.linear.FieldMatrix;
> import org.apache.commons.math3.linear.MatrixUtils;
> import org.apache.commons.math3.util.BigReal;
> public class REPREX {
> public static void main(String[] args) {
> BigReal[][] leftMatrixData = new BigReal[][]{
> {new BigReal(1), new BigReal(0), new BigReal(0), new BigReal(0)},
> {new BigReal(1), new BigReal(0), new BigReal(1), new BigReal(0)},
> {new BigReal(1), new BigReal(1), new BigReal(0), new BigReal(0)},
> {new BigReal(1), new BigReal(1), new BigReal(1), new BigReal(1)},
> };
> FieldMatrix<BigReal> leftMatrix = MatrixUtils.createFieldMatrix(leftMatrixData);
> FieldMatrix<BigReal> leftMatrixInverse = new FieldLUDecomposition<>(leftMatrix)
> .getSolver()
> .getInverse();
> // Exception in thread "main" org.apache.commons.math3.exception.MathArithmeticException: zero not allowed here
> // at org.apache.commons.math3.util.BigReal.divide(BigReal.java:255)
> // at org.apache.commons.math3.util.BigReal.divide(BigReal.java:39)
> // at org.apache.commons.math3.linear.FieldLUDecomposition.<init>(FieldLUDecomposition.java:160)
> // at stackoverflow.math.matrix.REPREX.main(REPREX.java:18)
> }
> }
> {code}
> h3. Possible reason:
> In {{FieldLUDecomposition}} line 130-133
> {code:java}
> if (lu[nonZero][col].equals(field.getZero())) {
> // try to select a better permutation choice
> ++nonZero;
> }
> {code}
> Which produce incorrect result when {{lu[nonZeror][col]}} the BigDecimal val has different scale
> to {{field.getZero()}} scale. as the {{BigReal#equals}} is comparing using {{BigDecimal#equals}}
> h3. Workaround
> I tried to copy class {{BigReal}} and {{BigRealField}} to {{FixBigReal}} and {{FixBigRealField}} and replace all {{BigReal}} to {{FixBigReal}} inside. Then override {{FixBIgReal#equals}} as
> {code:java}
> @Override
> public boolean equals(Object other) {
> if (this == other) {
> return true;
> }
> if (other instanceof FixBigReal) {
> return d.compareTo(((FixBigReal) other).d) == 0;
> }
> return false;
> }
> {code}
> Then the below program will not throw error
> {code:java}
> import org.apache.commons.math3.linear.FieldLUDecomposition;
> import org.apache.commons.math3.linear.FieldMatrix;
> import org.apache.commons.math3.linear.MatrixUtils;
> import org.apache.commons.math3.util.BigReal;
> public class MVE {
> public static void main(String[] args) {
> FixBigReal[][] leftMatrixData = new FixBigReal[][]{
> {new FixBigReal(1), new FixBigReal(0), new FixBigReal(0), new FixBigReal(0)},
> {new FixBigReal(1), new FixBigReal(0), new FixBigReal(1), new FixBigReal(0)},
> {new FixBigReal(1), new FixBigReal(1), new FixBigReal(0), new FixBigReal(0)},
> {new FixBigReal(1), new FixBigReal(1), new FixBigReal(1), new FixBigReal(1)},
> };
> FieldMatrix<FixBigReal> leftMatrix = MatrixUtils.createFieldMatrix(leftMatrixData);
> FieldMatrix<FixBigReal> leftMatrixInverse = new FieldLUDecomposition<>(leftMatrix)
> .getSolver()
> .getInverse();
> }
> }
> {code}
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