Hi, On Wed, Dec 02, 2009 at 11:49:24PM -0800, smichr wrote: > > Is gcdfactor() any different from the following? > > > > In [1]: f = x**2*exp(x)+exp(x+y)*x/y > > > > In [2]: f > > Out[2]: > > x + y > > 2 x x⋅ℯ > > x ⋅ℯ + ──────── > > y > > > > In [3]: factor(f) > > Out[3]: > > ⎛ y⎞ > > ⎜ ℯ ⎟ x > > x⋅⎜x + ──⎟⋅ℯ > > ⎝ y ⎠ > > > > In this case, no. But gcdfactor would do nothing to 1-x**2 whereas > factor would return (1+x)*(1-x). Removing a common factor from all > terms before beginning the formal factoring process makes the regular > factoring a lot easier. I think the place for this type of function is > in simplify. It's like collect but it's not collecting for a given > term, it's collecting from every term whatever is in common and can be > extracted multiplicatively. >
I see your point. There is however terms_gcd() method in new Poly class which does the thing, e.g.: In [5]: factor(x**3*y-x*y**3) Out[5]: x⋅y⋅(x - y)⋅(x + y) In [6]: Poly(x**3*y-x*y**3).terms_gcd() Out[6]: ((1, 1), Poly(x**2 - y**2, x, y, domain='ZZ')) The last line should be interpreted as x**1*y**1 * (x**2 - y**2), so no factorization is performed. Currently there is no terms_gcd() function which would return Basic expression, as factor() does, but this is trivial to implement. Moreover, terms_gcd() is being used as a preprocessing procedure in factor(). Also note that you can pass `expand=False` to Poly and most polynomial manipulation functions, to keep input expression intact, e.g.: In [11]: Poly((x-1)*y**2 - (x-1)*y).terms_gcd() Out[11]: ((0, 1), Poly(x*y - x - y + 1, x, y, domain='ZZ')) In [12]: Poly((x-1)*y**2 - (x-1)*y, expand=False).terms_gcd() Out[12]: ((1, 1), Poly(-y + 1, 1 - x, y, domain='ZZ')) > -- > > You received this message because you are subscribed to the Google Groups > "sympy-patches" group. > To post to this group, send email to sympy-patc...@googlegroups.com. > To unsubscribe from this group, send email to > sympy-patches+unsubscr...@googlegroups.com. > For more options, visit this group at > http://groups.google.com/group/sympy-patches?hl=en. > > -- Mateusz
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