Great! Thank you. But expr.is_zero always implies, that simplified expr equals 0. Correct?
On Friday, March 19, 2021 at 3:51:31 PM UTC+2 Oscar wrote: > On Fri, 19 Mar 2021 at 13:19, Paul Royik <distan...@gmail.com> wrote: > > > > Is there a difference between checking b.is_zero or b == 0? > > Yes, there is. > > Checking is_zero is part of the core assumptions system that will run > a bunch of tests to try and determine if the expression is zero or not > and will ultimately return True, False or None with None meaning > "unknown". When checking with == 0 you are checking structural > equality so you will get True if the expression is precisely zero and > False otherwise but the expression might still be mathematically zero: > > In [12]: expr1 = sin(1)**2 + cos(1)**2 - 1 > > In [13]: print(expr1.is_zero) > None > > In [14]: print(expr1 == 0) > False > > Usually the interesting part about is_zero is distinguishing between > when it returns False and None. Knowing that an expression is > definitely not zero (is_zero = False) allows simplifications that are > not possible for an expression that is possibly zero (is_zero = None) > > It's unusual that an expression that is not structurally zero will > have is_zero = True (since it would usually have simplified to 0 > automatically) but it can happen particularly with algebraic > expressions: > > In [26]: phi = GoldenRatio > > In [27]: expr2 = phi**2 - phi - 1 > > In [28]: expr2 > Out[28]: > 2 > -φ - 1 + φ > > In [29]: expr2.is_zero > Out[29]: True > > In [30]: simplify(expr2) > Out[30]: 0 > > > Oscar > -- You received this message because you are subscribed to the Google Groups "sympy" group. To unsubscribe from this group and stop receiving emails from it, send an email to sympy+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/sympy/3784b7ac-f54d-499b-b65a-8f7b9d565b40n%40googlegroups.com.
