You have done a great job highlighting some of the things that are
easy in mathematica and hard in sage. I don't see any answer to your
points in the comments below. I suspect that a fairly serious rewrite
of symbolic expressions will be necessary at some point to help this
situation, but I don't think that it is un-doable in python.
Cheers,
M. Hampton
On Aug 22, 8:21 am, David Philp <[EMAIL PROTECTED]> wrote:
> On 22/08/2008, at 5:27 PM, William Stein wrote:
>
>
>
> > On Thu, Aug 21, 2008 at 11:28 PM, David Philp
> > <[EMAIL PROTECTED]> wrote:
>
> >> I hope one can't own such things but I don't want a legal fight.
>
> > If I were afraid, then Sage would be nowhere today.
>
> I just don't think Mathematica reimplementation is a worthy enough
> thing that it's worth risking a legal fight with Wolfram. There are
> other ways to make Sage really good.
>
> >> Otherwise, I agree. A mathematica-like parser would be useful.
> >> Though I'd be surprised if the concepts map across well enough for it
> >> to be anything other than an ugly hack.
>
> > Why?
>
> I don't think it's useful for me to keep going much more until I know
> more about sage. But I will explain where the bad feeling came from:
>
> All the explanations that "sage can do that" have involved python
> lists, because I used names and examples like 'data = {1, 2, 3}'. But
> the power of ReplaceAll (the /. operator) is that it places no
> requirements on the form of the 'data' argument.
>
> I.e. the example:
> [(0 if d < 0 else d) for d in data]
>
> is an illustration of how to write a for-each expression in python,
> but it has nothing much to do with ReplaceAll. The difference is that
> ReplaceAll is used for transforming 'data' not 'the elements of data'.
>
> E.g.
> x + a*y + z[w + v] /. Plus -> List
>
> yields {x, a y, z[{v, w}]} (That sort of manipulation has been useful
> to me sometimes.)
>
> It reads much the same as before: expr, but with sums replaced by lists.
>
> If someone proposes an implementation I can try and shoot it down or
> improve it. But I don't know sage well enough to know whether there
> is an obvious way to do it all. My guess is that this is a natural
> task for Lisp and the wrong task for Python.
>
> D
>
> ==================================
> David J Philp
> Postdoctoral Fellow
> National Centre for Epidemiology and Population Health
> Building 62, cnr Mills Rd & Eggleston Rd
> The Australian National University
> Canberra ACT 0200 Australia
>
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