Summary: logical operations & double precision

[Yuelin Li <yuelin@mail.med.upenn.edu>]

Sorry about my earlier summary.  It got garbled somehow.  Thanks to Jerry 
W. Lewis, James Holtman, Alan Zaslavsky, Luciano Molinari, Andy Liaw, David 
L Lorenz, Frank Harrell.  Frank Harrel points out that this is an IFAQ 
(incredibly frequently asked question).  A search of the S-news archive or 
a google.com search should provide useful help.
The solutions include incorporating roundoff tolerance, e.g, if(abs(x-1) <= 
1e-7), which I did and was hoping to avoid; or use the function round(x, 
digits=14) to handle the precision before comparisons.
Yuelin Li.