simplifying ^ fails, on exact numerical constants in Mathematica 5.0
- To: mathgroup at smc.vnet.net
- Subject: [mg61148] simplifying ^ fails, on exact numerical constants in Mathematica 5.0
- From: "Richard J. Fateman" <fateman at eecs.berkeley.edu>
- Date: Tue, 11 Oct 2005 03:22:17 -0400 (EDT)
- Organization: UC Berkeley
- Sender: owner-wri-mathgroup at wolfram.com
Consider f[x_, y_, n_] := (x^n)^(y/n) For x, y, positive rational numbers and n an integer this should compute exactly the same as x^y. And indeed this seems to be the case for f(1/4+1/10^18, 1/2, n) when n is 1,2,3 or 4. But it comes up with a different answer when n is 5 or more (using Mathematica 5.0). Are the answers different? N[%-%%,1000] checks numerical equality, but this gives an meprec error.... Simplify[..] does not simplify to zero. FullSimplify does better, if you are willing to wait long enough, (or n is small enough) and returns 0. Can a CAS do this right and fast? RJF