[
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.
--
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.
To unsubscribe, e-mail: [email protected]
For queries about this service, please contact Infrastructure at:
[email protected]
Issue Time Tracking
-------------------
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}
--
This message was sent by Atlassian Jira
(v8.3.4#803005)
