Aaron S. Meurer a écrit :
> Use cse() (common subexpression elimination). It will replace the
> logs with dummy variables, which you can then see is a polynomial.
> In [8]: cse((log(x) + 1)-((log(x)**3+7)))
> Out[8]: ([(x0, log(x))], [-6 + x0 - x0**3])
>
Why the ioutput is like this ? I've tried the folloowing :
=========================================
import sympy
x = sympy.Symbol('x')
x0 = sympy.Symbol('x0')
y = sympy.Symbol('y')
f = [ sympy.sympify('log(x)**2 + cos(y)*log(x)*(1+log(x))'),
sympy.sympify('log(x)**2 + 2*x') ]
for i in range(len(f)):
test = sympy.cse(f[i])
print test
=========================================
This gives :
-----------------------------------------------
([(x0, log(x))], [x0*(1 + x0)*cos(y) + x0**2])
([], [2*x + log(x)**2])
-----------------------------------------------
FIRST QUESTION
So why [(x0, log(x))] is not simply (x0, log(x)) ? Same
question for [x0*(1 + x0)*cos(y) + x0**2] ?
SECUND QUESTION
Is there a way to know if expression is a polybom regarding
to two or more functions like for example log(x)**2 +
cos(y)*log(x)*(1+log(x)) ?
Best regards.
Christophe
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