>
> We have two implementations of univariate Laurent series. One of them
> fails to compute all terms of degree <= 0 of the Laurent series 0. See
> demonstration below.
>
> https://github.com/fricas/fricas/blob/master/src/algebra//suls.spad#L117
>
> Problem seems to be that SULS computes the order of its input and fails
> to match the specification of order(l, 0).
>
> http://fricas.github.io/api/UnivariatePowerSeriesCategory.html#l-univariate-power-series-category-order
>
> order : % -> Expon
> ++ \spad{order(f)} is the degree of the lowest order non-zero
> ++ term in f.
> ++ This will result in an infinite loop if f has no non-zero terms.
> order : (%, Expon) -> Expon
> ++ \spad{order(f, n) = min(m, n)}, where m is the degree of the
> ++ lowest order non-zero term in f.
>
> Well, perhaps even the documentation is bad, since it is not really
> clear whether for f=0 and n=0, m is infinity and min(infinity, 0) is
> supposed to be 0, i.e. whether min refers to an implemented function min
> or to the (mathematical) min used in Z\cup\{\infty\}.
I think this is reasonably clear, in particular when you compare
the two definitions: the second version is supposed to finish
computation once it is clear that there are no nonzero terms of
order smaller than n (which agrees with mathematical definition
using min in Z\cup\{\infty\}).
>
> IMHO, the implementation of iOrder is wrong.
>
> https://github.com/fricas/fricas/blob/master/src/algebra//sups.spad#L284
>
> Shouldn't it rather be something like this?
>
> iOrder(st, n, refer) ==
> explicitlyEmpty? st => n
> ...
Yes, this is place to change, but the fix I commited needs
a second line.
--
Waldek Hebisch
[email protected]
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