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https://issues.apache.org/jira/browse/NUMBERS-163?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17364188#comment-17364188
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Gilles Sadowski commented on NUMBERS-163:
-----------------------------------------
bq. FMA is a lot more complicated to implement than the summation performed in
LinearCombination.
>From a design (API/implementation) POV, and following up on Matt's proposal,
>could we provide a class that mimics FMA usage (even if not all its
>requirements)?
{code}
public class FMA implements DoubleSupplier {
// ... state?
private FMA(double m1, double m2, double a) {
// ...
}
public FMA.of(double m1, double m2, double a) {
return new FMA(m1, m2, a);
}
public FMA.of(double m1, double m2, FMA other) {
final double a = ...
return new FMA(m1, m2, a);
}
// To allow usage in a collector.
public FMA fma(FMA other) {
// ... ?
}
@Override
public double getAsDouble() {
// The equivalent of Math.fma(m1, m2, a).
return ...
}
}
{code}
With the above API, is it possible to implement the combined functionality of
{{LinearCombination}} and {{Summation}}, with the same accuracy?
>From a usage POV,
{code}
LinearCombination.of(a1, v1, a2, v2);
{code}
would be replaced with
{code}
FMA.of(a1, v1, FMA.of(a2, v2, 0));
{code}
> Summation and LinearCombination Accumulators
> --------------------------------------------
>
> Key: NUMBERS-163
> URL: https://issues.apache.org/jira/browse/NUMBERS-163
> Project: Commons Numbers
> Issue Type: New Feature
> Reporter: Matt Juntunen
> Priority: Major
> Time Spent: 0.5h
> Remaining Estimate: 0h
>
> It would be useful to have simple accumulator classes in {{Summation}} and
> {{LinearCombination}} to perform extended precision operations on arbitrary
> collections of values without requiring conversion to {{double[]}}. Ex:
> {code:java}
> Summation.Accumulator sum= Summation.accumulator(1d);
> sum.add(x)
> .add(y)
> .add(z)
> .add(w);
> double sumResult = sum.get();
> LinearCombination.Accumulator comb = LinearCombination.accumulator(1d);
> comb.add(x, scale)
> .add(y, scale)
> .add(z, scale)
> .add(w, scale);
> double combResult = comb.get();
> {code}
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