Mateusz,
thanks for your quick reply.
Your suggestion handles this case well. If I have a function f has N
children in the tree,
e.g. tree = ('add', 'x', ('f', 'a1', 'a2', 'a3', 'a4', ..., 'a100'))
how can I express mapping[f](a1, a2, ...an)? N here could be
arbitrary and I don't know its value before hand.
thanks a lot
Jeff
On Dec 30, 5:35 pm, Mateusz Paprocki <matt...@gmail.com> wrote:
> Hi,
>
> On Thu, Dec 30, 2010 at 01:34:07PM -0800, Jeff Cen wrote:
>
> > Hi,
>
> > Suppose I have already had an expression tree in a tree structure
> > (like a nested list, say ['add', 'x', ['subtract', 'x', 'y']]), I
> > would like to convert it to sympy expression and simplify it in sympy.
>
> > When I read my tree structure, I first create an Add function. Then
> > how can I append x and the rest?
>
> A simple helper function will do the job, e.g.:
>
> In [1]: from sympy import *
>
> In [2]: import operator
>
> In [3]: mapping = {'add': operator.add, 'subtract': operator.sub}
>
> In [4]: tree = ('add', 'x', ('subtract', 'x', 'y'))
>
> In [5]: def convert(tree):
> ....: op, a, b = tree
> ....: if isinstance(a, tuple): a = convert(a)
> ....: else: a = sympify(a)
> ....: if isinstance(b, tuple): b = convert(b)
> ....: else: b = sympify(b)
> ....: return mapping[op](a, b)
> ....:
>
> In [6]: convert(tree)
> Out[6]: -y + 2⋅x
>
> > thanks
>
> > Jeff
>
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>
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