Thanks for the temporary fix to ndiv.
However even with this fix cse in bleeding edge sympy gives:
[pg01**2/pg00**2, 1.0 - 2*pg01/pg00, pg01*(1.0 - pg01/pg00)]
[(x0, -pg01/pg00)]
[pg01**2/pg00**2, 1.0 - 2*pg01/pg00, pg01*(x0 + 1.0)]
whereas cse in sympy 7.1 gives:
[pg01**2/pg00**2, 1.0 - 2*pg01/pg00, pg01*(1.0 - pg01/pg00)]
[(x0, 1/pg00), (x1, pg01*x0)]
[x1**2, -2*x1 + 1.0, pg01*(-x1 + 1.0)]
I think sympy 7.1 result is better.
Larry Wigton
On Thursday, September 6, 2012 12:55:44 PM UTC-7, Larry Wigton wrote:
>
> Python code using cse from sympy:
>
> from sympy import *
> x=Symbol('x')
> y=Symbol('y')
> eq1 = 5*x**3*y**2 + y**3
> eq2 = 4*x**2*y**3 + y**2
> eq = [eq1,eq2]
> print eq
> (red,rep) = cse(eq)
> print red
> print rep
> eq = [eq2,eq1]
> print eq
> (red,rep) = cse(eq)
> print red
> print rep
>
> ***********************************************
>
> Output from the code:
>
> [5*x**3*y**2 + y**3, 4*x**2*y**3 + y**2]
> [(x0, y**3), (x1, x0**(2/3))]
> [5*x**3*x1 + x0, 4*x**2*x0 + x1]
>
> [4*x**2*y**3 + y**2, 5*x**3*y**2 + y**3]
> [(x0, y**2), (x1, x0**(3/2))]
> [4*x**2*x1 + x0, 5*x**3*x0 + x1]
>
> **********************************************
>
> The introduction of the powers 2/3 and 3/2 is not acceptable.
>
> For one thing in Fortran 2/3 will beocme 0 and 3/2 will become 1.
>
> Even if we make 2 and 3 floating point numbers this is not efficient.
>
> Also if we take x0=y**2 and then try to compute y**3 using x0**(1.5)
> we get the wrong answer in the case y is negative.
>
> ************************************************************
>
> Is there some way to run cse to avoid this undesirable behavior?
>
> Can cse be modified to avoid this undesirable behavior?
>
>
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