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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