On Fri, Oct 31, 2014 at 11:45:19AM -0700, Richard Fateman wrote:
> For closed-source commercial programs it is possible to report a bug and
> have an expert resolve the problem accurately and promptly.
Why this is impossible for open-source programs?
> How likely is this?? I think it depends on
> (a) how important the bug is
> (b) how important the person reporting the bug is
> (c) how much money/lives/etc depend on the bug being fixed.
Apparently, Spain universities doesn't matter for the
Wolfram Research. Or they count "a serious mistake on the
determinant operation" as not important.
Worst news - there is an inevitable vendor lock-in. You can't give
your money someone else (but only single "group of experts", mostly
anonymous for you) to fix the issue.
> As for bugs, consider the expression (in mathematica syntax)
> Sum[x^i, {i, 0, n}]
> which is computed in closed form, but consider specific values,
> say
> x=2, n=-4.
> for which the correct answer is -7/8 even though Sum[2^i,{i.0,-4}] comes
> out 0.
> Now try it in other programs.
Well, SymPy doesn't have this inconsistency:
In [3]: k, n = symbols('k, n', integer=True)
In [4]: f = symbols('f', cls=Function)
In [5]: summation(2**k, (k, 0, -4))
Out[5]: -7/8
In [6]: summation(2**k, (k, 0, n))
Out[6]:
n + 1
2 - 1
In [7]: _.subs(n, -4)
Out[7]: -7/8
The issue here is that Mathematica count n as positive:
In[9]:= Sum[f[i], {i, 0, -2}]
Out[9]= 0
While SymPy uses the Karr convention instead:
In [10]: summation(f(k), (k, 0, -4))
Out[10]: -f(-3) - f(-2) - f(-1)
(I don't remember, probably this will be invalid too for infinite n. So,
maybe we have a very similar issue for n=-oo due to implicit assumption that n
is a
finite number.)
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