On 11 January 2012 14:45, Aaron Meurer <[email protected]> wrote: > I think it's reasonable to keep it as it is now. The reason is that > we can then say that expr.subs(x, sol) will give 0. This wouldn't > hold for solutions based on continuous extension. > > I was going to say that you could use cancel() to get rid of these, > but that only holds for rational functions. For example, sin(x)/x - 1 > has a "zero" at x = 0, but the only way to get this from solve is to > give check=False. So I think we should keep it like this, but document > that if you want the others, you should pass check=False to solve(). > I've added a documentation issue http://code.google.com/p/sympy/issues/detail?id=2981
> > In [31]: solve(sin(x)/x, x) > Out[31]: [] > > In [32]: solve(sin(x)/x, x, check=False) > Out[32]: [0] > > This is kind of analogous the force option to many of the simplify() > options. By default, we are rigorous, and only do the transformation > if it is valid. But we allow force=True to give the algebraic > solution. Rigorously, x/(x**2 + x) is not equal to 1/(x + 1), but many > fields consider them to be equivalent for the sake of simplification > of the theory. > > Aaron Meurer > > On Wed, Jan 11, 2012 at 6:28 AM, Chris Smith <[email protected]> wrote: > >> No, no, it is continuous because the limit when x-->0 exists (equals > >> 0), and the same as a value of function at this point, 0**2/0 (which by > >> definition is equal 0). > >> > > In earlier discussions we decided not to allow solutions of equations > > that set any denominator to zero even though the limit at that point > > might exist. I wonder if that should be changed so that if the limit > > exists and is the same from both directions the solution is returned; > > > >>>> e=(x**2*(1/x - z**2/x)) > >>>> e.expand() > > -x*z**2 + x > >>>> solve(_,x) > > [0] > >>>> solve(e,x) > > [] > >>>> e.subs(x,0) > > 0 > > > > -- > > You received this message because you are subscribed to the Google > Groups "sympy" group. > > To post to this group, send email to [email protected]. > > To unsubscribe from this group, send email to > [email protected]. > > For more options, visit this group at > http://groups.google.com/group/sympy?hl=en. > > > > -- > You received this message because you are subscribed to the Google Groups > "sympy" group. > To post to this group, send email to [email protected]. > To unsubscribe from this group, send email to > [email protected]. > For more options, visit this group at > http://groups.google.com/group/sympy?hl=en. > > -- You received this message because you are subscribed to the Google Groups "sympy" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/sympy?hl=en.
