Can you anticipate all the possible ways of misusing a command, and
catch them all
with a suitable error message? I think that's pretty hard with a
system that has essentially
free-form input of any length, attached to fairly vague semantics
(like --- let's see what
Maxima does with this ---).
RJF
On Aug 18, 8:37 pm, Robert Bradshaw <rober...@math.washington.edu>
wrote:
> On Aug 18, 2009, at 6:55 PM, Golam Mortuza Hossain wrote:
>
>
>
>
>
> > Hi,
>
> > On Tue, Aug 18, 2009 at 9:27 PM, William Stein<wst...@gmail.com>
> > wrote:
>
> >>> ----------
> >>> sage: f(x) = function('f',x)
>
> >>> sage: f(x).integral(x)
> >>> integrate(f(x), x)
>
> >>> sage: f(x).integral(x^2)
> >>> x^2*f(x)
> >>> -----------
>
> >> Indeed, what does that mean? If forced to, I would interpret this as
>
> >> int f(x) d(x^2) = int f(x) 2 x dx
> >> = 2x integrate(f(x),x)
>
> >> So I think the Sage/Maxima answer of x^2*f(x) is bizarre.
>
> >> Matheamatica just considers this input to be invalid:
>
> >> sage: mathematica.eval('Integrate[f[x],x^2]')
>
> >> 2
> >> Integrate::ilim: Invalid integration variable or limit(s) in x .
>
> >> 2
> >> Integrate[f[x], x ]
>
> >> Unless you can give a explanation of what you want integrating wrt
> >> x^2
> >> to mean, I think we should also raise an error in Sage.
>
> > I tried that input out of curiosity during testing. I was expecting
> > a TypeError but instead I got an answer !!
>
> > I agree, we should raise an error. Ironically, in "calculus.py"
> > the raise
> > error line (556) has been commented out for some reason.
> > -----------
> > elif not is_SymbolicVariable(v):
> > v = var(repr(v))
> > #raise TypeError, 'must integrate with respect to a variable'
>
> Probably var(repr(var)) is the wrong thing to do here... I have a
> feeling I've seen this code before.
>
> - Robert
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