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https://issues.apache.org/jira/browse/MATH-863?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13460348#comment-13460348
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Sébastien Brisard commented on MATH-863:
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{quote}
Let's wait for Juliens's tests and adjust the javadoc accordingly.
We may end up having some classes supporting non-commutative fields and other
requiring commutative fields and just state that in the doc, or we may add a
CommutativeField marker interface which would extend Field, or we could add a
isCommutative method in the Field interface and check that were needed. I'm not
sure the Java typing mechanism is sufficient, so either simple documentation or
runtime checks may be helpful.
{quote}
These are all safe suggestions from my point of view. I have to say I always
find it difficult to predict what's going to happen with generics, but maybe we
could define a {{NonCommutativeFieldElement}}, move all methods from
{{FieldElement}} to {{NonCommutativeFieldElement}}, and have {{FieldElement}}
extend {{NonCommutativeFieldElement}}. This way, all classes that operate on
field elements would by default not operate on non-commutative field elements.
After careful check, if appropriate, we could change the signature
{{class A<T extends FieldElement<T>>}} to {{class A<T extends
NonCommutativeFieldElement<T>>}}. Again, I'm not sure that would work.
Otherwise, the {{isCommutative()}} method should be invoked in the constructor
of {{class A}}.
> new Quaternion class added in complex package
> ---------------------------------------------
>
> Key: MATH-863
> URL: https://issues.apache.org/jira/browse/MATH-863
> Project: Commons Math
> Issue Type: New Feature
> Affects Versions: 3.1
> Reporter: Julien Anxionnat
> Attachments: quaternion_adjustments.patch, quaternion.patch,
> quaternion_v2.patch
>
> Original Estimate: 0h
> Remaining Estimate: 0h
>
> This patch provides a new class for the mathematical object "Quaternion" in
> the complex package.
> This quaternion is considered as a mathematical object (the Hamilton's
> hypercomplex number).
> Note that it's not a rotation quaternion which has to be a quaternion of norm
> one. Although this feature could be used for a getter in the Rotation class.
> This patch provides also some improvements in Precision class : a "double
> comparison epsilon" and a method to compute relative comparison.
> (Please, note that's it's my first contribution, and I apologize in advance
> for my mistakes…)
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