Note: discussion at https://github.com/golang/go/issues/36536 . TL;DR fused
floating point multiply-add gives higher precision results.
On Sunday, January 12, 2020 at 8:19:54 PM UTC-8, kortschak wrote:
>
> I am going through failures that I see in Gonum tests when we build on
> arm64 (Travis now provide this).
>
> In many cases there are slight differences that I'm OK with adding a
> tolerance to accept, but in one case (stat.ROC[0][1]) I see an error
> that can be completely avoided by changing the expression from what is
> at [1] to
>
> ```
> for i := range tpr {
> tpr[i] = 1 - tpr[i]/nPos
> fpr[i] = 1 - fpr[i]/nNeg
> }
> ```
>
> Should I expect `inv := 1/c; v *= inv` and `v /= c` to give the same
> results for reasonable cases? (or at least to match the behaviour on
> amd64/386/arm - which all agree).
>
> thanks
> Dan
>
> [0]https://godoc.org/gonum.org/v1/gonum/stat#ROC
> [1]
>
> https://github.com/gonum/gonum/blob/683ee363d56e77121c6640345bb9d40644f02a1f/stat/roc.go#L107-L114
>
>
>
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