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.
HTH,
Colin
On Apr 30, 5:05 pm, Ondrej Certik <ond...@certik.cz> wrote:
> On Thu, Apr 30, 2009 at 3:01 AM, Colin Gillespie
<c.gilles...@ncl.ac.uk> wrote:
>
> > Hi,
>
> > In the code:
>
> >>>> x=sympify('pow(PZ,2)')
> >>>> x
> > pow(PZ, 2)
> >>>> Poly(x,Symbol('PZ'))
> > 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 402, in __new__
> > terms = Poly._decompose(poly, *symbols)
> > File "/data/ncsg3/pythonModules/lib/python2.5/site-packages/
> > sympy-0.6.4-py2.5.egg/sympy/polys/polynomial.py", line 545, in
> > _decompose
> > raise PolynomialError("Can't decompose %s" % factor)
> > sympy.polys.polynomial.PolynomialError: Can't decompose pow(PZ, 2)
>
> > Is this expected behaviour or should sympify convert pow(PZ,2) to
> > PZ2?
>
> The sympify is indeed wrong. Could you debug what kind of "pow" it
> generated? It's something different than if you type pow(PZ, 2)
> yourself, as you can see here:
>
> In [1]: sympify("pow(PZ, 2)")
> Out[1]: pow(PZ, 2)
>
> In [2]: var("PZ")
> Out[2]: PZ
>
> In [3]: pow(PZ, 2)
> Out[3]:
> 2
> PZ
>
> Thanks,
> Ondrej
--
Dr Colin Gillespie
http://www.mas.ncl.ac.uk/~ncsg3/
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