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Re: Possible bug in Floor function?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg132349] Re: Possible bug in Floor function?
  • From: Bill Rowe <readnews at sbcglobal.net>
  • Date: Sat, 15 Feb 2014 23:14:57 -0500 (EST)
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  • Delivered-to: l-mathgroup@wolfram.com
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On 2/15/14 at 4:02 AM, s.nesseris at gmail.com (psycho_dad) wrote:

>I think I may have stumbled upon a possible bug in Floor. Evaluating
>the following gives the correct result:

>Floor[Log[10, 100.]]
>2

>Evaluating it with a replacement and //N gives a message and the
>wrong result:

>Floor[Log[10, x]] /. x -> 100 // N

>1

The problem isn't with Floor. The issue is simply the usage of
machine precision arithmetic. That is

In[11]:= RealDigits[Log[10, x] /. x -> 100 // N]

Out[11]= {{1,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9},1}

As you can see, the result is just slightly less than 2. So, the
result Floor returns is correct




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