Hello,
I have been using sympy a lot recently (economical modelling) and
(while it's a great software) I found a strange behavior when doing
substitution : it is not respecting operators priority. I think it's
because it works sequentially with all its arguments, but it leads to
somewhat surprising results.
In the following session, I was expecting to get the square root of 4,
i.e. 2, but instead the program is taking to fractional exponents of a
negative number which has a non unique definition.
In [1]: from sympy import *
In [2]: var('a b')
Out[2]: (a, b)
In [3]: eq = (a/b)**0.5
In [4]: eq.subs({a:-2,b:-0.5})
Out[4]: -2.00000000000000
As a workaround, I found myself lambdifying expressions, but I know
it's a bad workaround working only when substituion is made with
respect to all arguments. What do you suggest ?
Best,
Pablo
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