Hi,
I think that the expected behaviour would be for pow(x,2) to return
x^2, as opposed to a general function. Otherwise, it would be
inconsistent with how 'sin' and 'exp' are handled (for example).
Cheers
Colin
On May 1, 7:02 pm, Ondrej Certik <ond...@certik.cz> wrote:
> On Fri, May 1, 2009 at 10:45 AM, Colin Gillespie <c.gilles...@ncl.ac.uk>
> wrote:
>
> > Hi Ondrej,
>
> > I've tried to figure out exactly where the errors lies, but don't have
> > anything concrete. Here's what I have come up with:
>
> >> >> y=Symbol("pow(A,2)")
> >> >> Poly(y,y)
> > Poly(pow(A,2), pow(A,2))
>
> > Seems OK.
>
> >> >> x=sympify("pow1(PZPZ)")
> >> >> help(x)
> > Help on pow1 in module sympy.core.function object:
>
> > class pow1(Function)
> > | Base class for applied functions.
> > | Constructor of undefined classes.
> > | | Method resolution order:
> > | pow1
> > | Function
> > | sympy.core.basic.Basic
> > | sympy.core.assumptions.AssumeMeths
> > | __builtin__.object
> > <snip>
> >> >> Poly(x,x)
> > Traceback (most recent call last):
> > File "<stdin>", line 1, in <module>
> > File "/data/ncsg3/pythonModules/lib/python2.5/site-packages/
> > sympy-0.6.4-py2.5.egg/sympy/polys/polynomial.py", line 310, in __new__
> > raise SymbolsError("Invalid symbols: %s" % (symbols,))
> > sympy.polys.polynomial.SymbolsError: Invalid symbols: (pow1(PZPZ),)
>
> > Notice that I've used 'pow1' not 'pow'. I think that sympify creates a
> > function 'pow1' that Poly doesn't know what to do with. When we change
> > pow1 -> pow we get the same error, so essentially I think that pow
> > isn't being associated with power.
>
> Yes, you have figured that out, thanks!
>
> Indeed, sympify just creates functions for what it thinks are functions.
>
> So now the question is --- do you want sympify to recognize pow() as a power?
>
> Ondrej
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