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https://issues.apache.org/jira/browse/MATH-306?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Joerg Huber updated MATH-306:
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Description:
The formula that 'divide' wants to implement is
( a + bi ) / ( c + di ) = ( ac + bd + ( bc - ad ) i ) / ( c^2 + d^2 )
as correctly written in the description.
When c == 0.0 this leads to the special case
( a + bi ) / di = ( b / d ) - ( a / d ) i
But the corresponding code is:
if (c == 0.0) {
return createComplex(imaginary/d, -real/c);
}
The bug is the last division -real/c, which should obviously be -real/d.
was:
The formula that 'divide' wants to implement is
a + bi ac + bd + (bc - ad)i
----------- = -------------------------
c + di c<sup>2</sup> + d<sup>2</sup>
as correctly written in the description.
When c == 0.0 this leads to the special case
a + bi b - a i
----------- = ------------
di d
But the corresponding code is:
if (c == 0.0) {
return createComplex(imaginary/d, -real/c);
}
The bug is the last division -real/c, which should obviously be -real/d.
Other layout and an additional formula conversion for better readability
> Method 'divide' in class 'Complex' uses a false formula for a special case
> resulting in erroneous division by zero.
> -------------------------------------------------------------------------------------------------------------------
>
> Key: MATH-306
> URL: https://issues.apache.org/jira/browse/MATH-306
> Project: Commons Math
> Issue Type: Bug
> Environment: all
> Reporter: Joerg Huber
>
> The formula that 'divide' wants to implement is
> ( a + bi ) / ( c + di ) = ( ac + bd + ( bc - ad ) i ) / ( c^2 + d^2 )
> as correctly written in the description.
> When c == 0.0 this leads to the special case
> ( a + bi ) / di = ( b / d ) - ( a / d ) i
> But the corresponding code is:
> if (c == 0.0) {
> return createComplex(imaginary/d, -real/c);
> }
> The bug is the last division -real/c, which should obviously be -real/d.
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