RE: Q: Union and precision.

*To*: mathgroup at smc.vnet.net*Subject*: [mg8548] RE: [mg8529] Q: Union and precision.*From*: Ersek_Ted%PAX1A at mr.nawcad.navy.mil*Date*: Sat, 6 Sep 1997 23:16:15 -0400*Sender*: owner-wri-mathgroup at wolfram.com

Oron wrote: | |How can I force Union to consider numbers equal in the current |precision as equal? Explanation: | |In:= a=SetPrecision[1.234567,2] |Out:= 1.2 | |In:= b=SetPrecision[1.234561,2] (* Notice difference *) |Out:= 1.2 | |In:= a==b |Out:= True | |In:= Union[{a,b}] |Out:= {1.2,1.2} (* !!! *) | |How does Union evaluates equalities? How can I force it to do it the right |way?? | | Union uses the setting for the SameTest Option to determine if two elements are "equal". By default it uses SameTest->Automatic. However, I don't know exactly what this does. You will get the results you want if you use the following: In:= Union[ {a,b}, SameTest->Equal ] Out= {1.2} Even better. you can add a line in your init.m file, and Union will always have the default (SameTest->Equal). Well first you have to restart Mathematica using the new init.m. Here is what you add to init.m. SetOptions[ Union, SameTest->Equal ] Ted Ersek