Hi Mike,
On 11/20/2013 10:31 AM, Mike Duigou wrote:
- Collectors averagingDouble could use the same @implNote as in DoublePipeline.
- DoublePipeline implementation could document the usage of the double array
indices.
- @summary in test.
I'll reflect these in the next iteration.
- I agree with Paul that refactoring as a testNG test would be nice.
While learning about testNG would be useful, I don't want to take that
on right at the moment ;-)
- I wondered at the mechanism for combining compensation values. Do you have a
reference which explains the correctness? I thought perhaps directly adding the
compensations together before doing compensated addition of the two sums might
be better.
One of the inquiries I have out to my numerical reviewer is how to best
combine two compensations.
In the code as written, from the perspective of one compensation, the
two doubles in the other other compensation are just two more double
values. So I think this is correct, if not ideal.
The compensation portion of one running sum could be of vastly different
magnitude than the compensation portion (or the high-order sum bits) of
the other sum. Therefore, I believe a direct combination of either (sum1
+ sum2) or (comp1 + comp2) would lose the numerical properties of
interest here.
Thanks for the feedback,
-Joe
Mike
On Nov 20 2013, at 00:21 , Joe Darcy <[email protected]> wrote:
Hi Paul,
On 11/18/2013 07:38 AM, Paul Sandoz wrote:
Hi Joe,
You can use the three arg form of collect for DoublePipeline.sum/average impls,
which is already used for average:
public final OptionalDouble average() {
double[] avg = collect(() -> new double[2],
(ll, i) -> {
ll[0]++;
ll[1] += i;
},
(ll, rr) -> {
ll[0] += rr[0];
ll[1] += rr[1];
});
return avg[0] > 0
? OptionalDouble.of(avg[1] / avg[0])
: OptionalDouble.empty();
}
That would be the most expedient way.
Thanks for the tip. For the moment, I'm feeling a bit expedient and used the
array-based approach in an iteration of the change:
http://cr.openjdk.java.net/~darcy/8006572.3/
