Re: Re: floor problems
- To: mathgroup at smc.vnet.net
- Subject: [mg8244] Re: [mg8151] Re: [mg8113] floor problems
- From: seanross at worldnet.att.net
- Date: Thu, 21 Aug 1997 21:17:01 -0400
- Sender: owner-wri-mathgroup at wolfram.com
Lou Talman wrote: > > The example I gave in my earlier post seems to show that multiplication of > floating point numbers isn't commutative. In fact, the problem is with > associativity, as I claimed. Here is the example I should have given: > > In[2]:= > ((.7 67 )10)-(.7 (67 10)) > > Out[2]= > \!\(5.68434188608080148`*^-14\) > > --Lou Talman You are thinking like an abstract mathematician rather than a computer programmer, scientist or engineer. For a number that is only has 15 digits of precision, 5.6*10^-14 is "zero". Multiplication of floating point numbers is associative--within the precision of the numbers. You have to learn to take things like that into account once the mathematics leaves your pencil and pad and is put on a digital machine like a computer or calculator.