Hi.
> >> >> + * MATH-803: it is not sufficient to loop through non zero
> >> >> entries of
> >> >> + * this only. Indeed, if this[i] = 0d and v[i] = 0d, then
> >> >> + * this[i] / v[i] = NaN, and not 0d.
> >> >> + */
> >> >> + final int n = getDimension();
> >> >> + for (int i = 0; i < n; i++) {
> >> >> + res.setEntry(i, this.getEntry(i) / v.getEntry(i));
> >> >> }
> >> >> return res;
> >> >> }
> >> >
> >> > I think that this renders the class potentially useless, if we assume
> >> > that
> >> > it is used when "large" vectors are needed.
> >> > Indeed, after this operation, all the entries will be stored; thus
> >> > cancelling the memory efficiency of the class, and probably making the
> >> > returned value slower than an "ArrayRealVector" instance for subsequent
> >> > operations.
> >> >
> >> I'm not sure that all entries would be stored (except if setEntry does
> >> not distinguish between zero values and non-zero values).
> >
> > The problem is when the common values are not the default one, like ...
> >
> >>
> >> > For every method that a "RealVector" argument, there should be a
> >> > specialized
> >> > implementation that take an "OpenMapRealVector".
> >> >
> >> > Also, couldn't we solve some of these problems if the value of the
> >> > default
> >> > entry was stored and mutable? E.g. if the default for "v" and "w" is
> >> > zero,
> >> > then the default for "v / w" will be "NaN".
> >
> > ... in this example.
> >
> Ooops, missed this one!
> Yes that was an improvement I was thinking of (in fact, the unit tests
> are already implemented with this idea in mind).
> This would allow efficient implementation of the cosine for example.
> I didn't think about the application you suggest, but I like this idea
> very much.
>
> How about we leave it as is for the time being, and we open a JIRA
> ticket for this improvement, explicitely mentioning that ebeDivide()
> and ebeMultiply() should be revisited in order to improve their
> efficiency?
I agree.
>
> This does not solve the whole issue, however, because if the default
> entry is zero, its sign is lost, and {finite value} / {zero} is of
> undetermined sign. Any idea regarding this point?
I guess that we could also keep a flag for the sign.
Best regards,
Gilles
P.S. Maybe that we should also have a look at how other libraries handle
this kind of issues.
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