This is clearly a bug, hopefully one that will be fixed soon.
Aside: symbolic manipulations are more robust when expressions involve
rational numbers instead of floating point numbers. For example:
y = a + Rational(1, 4)*b**2 + 1*b*c*x + 1*c**2*x**2
or
y = a + Rational('0.25')*b**2 + 1*b*c*x + 1*c**2*x**2
would avoid the issue.
Thanks for the report.
On Thursday, January 25, 2018 at 5:07:57 PM UTC-5, Chuck Ursenbach wrote:
>
> I'm using isympy from a recent anaconda3 installation. I find that factor
> is introducing a spurious factor of 0.25.
>
> If I run this:
>
> from sympy import *
> a,b,c,d,x,y = symbols('a,b,c,d,x,y')
> y = a + 0.25*b**2 + 1.0*b*c*x + 1.0*c**2*x**2
> print('factor')
> print(factor(y-a))
> print('expand')
> print(expand(y-a))
> print('factor difference')
> print(simplify(y-a-factor(y-a)))
> print('expand difference')
> print(simplify(y-a-expand(y-a)))
>
> then I get this:
>
> factor
> 1.0*(0.25*b + 0.5*c*x)**2
> expand
> 0.25*b**2 + 1.0*b*c*x + 1.0*c**2*x**2
> factor difference
> 0.1875*b**2 + 0.75*b*c*x + 0.75*c**2*x**2
> expand difference
> 0
>
>
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