Re: Re: Zero does not Equal Zero

*To*: mathgroup at smc.vnet.net*Subject*: [mg31302] Re: [mg31281] Re: Zero does not Equal Zero*From*: Otto Linsuain <linsuain at andrew.cmu.edu>*Date*: Sat, 27 Oct 2001 01:08:11 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

Perhaps this is relevant: With your definition of x and y In[13]:= FullForm[x-y] Out[13]//FullForm= 1.2`0.0366 and In[11]:= 0.\[Equal]0 Out[11]= True Otto Linsuain. On Fri, 26 Oct 2001, Adam Smith wrote: > The problem is that you specified a non-integer value for the number of digits > of precision "21.35". As shown below, if you set it equal to an integer things > work out as expected. I don't know what SetPrecision does intenally when it is > a non-integer, but I agree that something strange happens. > > In[1]:= > x=SetPrecision[1234567890123456789012, 21.35]; > y=x-6/5; > {x-y, x-y\[Equal]0} > > Out[3]= > {0.,False} > > In[4]:= > x=SetPrecision[1234567890123456789012, 21]; > y=x-6/5; > {x-y, x-y\[Equal]0} > > Out[6]= > {0.,True} > > > > > In article <9qokvl$mu2$1 at smc.vnet.net>, Ersek, Ted R says... > > > >Hello Group, > > > >I am using Mathematica Version 4.1.0.0 under Windows 98, but I suspect it > >makes no difference what platform is used. > > > >The following demonstrates an inconsistency with arbitrary precision > >arithmetic. The problem is that the criteria for deciding what numbers are > >displayed as zero is different from the criteria for deciding if a number > >equals zero. > > > > > >In[1]:= > > x=SetPrecision[1234567890123456789012, 21.35]; > > y=x-6/5; > > {x-y, x-y==0} > > > >Out[3]= > > {0., False} > > > > > >---------- > >For what it's worth, the next line shows that the precision of (x-y) is > >(0.0366) almost zero. > > > >In[4]= > > InputForm[x-y] > > > >Out[4]= > > 1.2`0.0366 > > > >----------- > >Regards, > > Ted Ersek > > Check Mathematica Tips, Tricks at > > http://www.verbeia.com/mathematica/tips/Tricks.html > > > > > > Adam Smith > Dept. of Physics > Hillsdale College > adam.smith at hillsdale.edu > >