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https://issues.apache.org/jira/browse/MATH-1617?focusedWorklogId=631445&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-631445
]
ASF GitHub Bot logged work on MATH-1617:
----------------------------------------
Author: ASF GitHub Bot
Created on: 30/Jul/21 02:10
Start Date: 30/Jul/21 02:10
Worklog Time Spent: 10m
Work Description: coveralls commented on pull request #192:
URL: https://github.com/apache/commons-math/pull/192#issuecomment-889576221
[](https://coveralls.io/builds/41769674)
Coverage increased (+3.0e-06%) to 90.478% when pulling
**f54ef1d2d1a3b060da56fdc6c9330d71926a849f on samabcde:MATH-1617** into
**8cd59b991eeb911d94b82504cff737bcafa1b660 on apache:master**.
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Issue Time Tracking
-------------------
Worklog Id: (was: 631445)
Time Spent: 40m (was: 0.5h)
> 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: 40m
> 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}} and {{FixBIgReal#hashcode }}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;
> }
> ...
> @Override
> public int hashCode() {
> return Double.hashCode(d.doubleValue());
> }
> {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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