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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Mateusz
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