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
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
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?
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