Re: Re: When Is Precision[ ] $MachinePrecision, And When Is It Not?

*To*: mathgroup at smc.vnet.net*Subject*: [mg47574] Re: [mg47525] Re: When Is Precision[ ] $MachinePrecision, And When Is It Not?*From*: Murray Eisenberg <murray at math.umass.edu>*Date*: Fri, 16 Apr 2004 05:20:59 -0400 (EDT)*Organization*: Mathematics & Statistics, Univ. of Mass./Amherst*References*: <c5dhrd$nqp$1@smc.vnet.net> <c5gg7l$att$1@smc.vnet.net> <200404150739.DAA11614@smc.vnet.net>*Reply-to*: murray at math.umass.edu*Sender*: owner-wri-mathgroup at wolfram.com

Evidently the exact value 2/3 on the right of N[2/3]==2/3 is converted to floating point before the comparison is made. (Same thing happens, for example, in 3.1 + 2/3) But: N[2/3]===2/3 False Look up == (or Equal) and === (SameQ) in the HelpBrowser. Harold Noffke wrote: > Bobby: > > Thanks for your examples. I thought about them, and found a very > short one which still bothers me, because the answer is not what I > expected ... > > In[1]:= N[2/3] > > Out[1]= 0.666667 > > In[2]:= N[2/3]==2/3 > > Out[2]= True > > In[3]:= ?== > lhs == rhs returns True if lhs and rhs are identical. > > Regards, > Harold > > -- Murray Eisenberg murray at math.umass.edu Mathematics & Statistics Dept. Lederle Graduate Research Tower phone 413 549-1020 (H) University of Massachusetts 413 545-2859 (W) 710 North Pleasant Street fax 413 545-1801 Amherst, MA 01003-9305

**References**:**Re: When Is Precision[ ] $MachinePrecision, And When Is It Not?***From:*Harold.Noffke@wpafb.af.mil (Harold Noffke)