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Re: Possible bug in Floor function?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg132347] Re: Possible bug in Floor function?
  • From: Bob Hanlon <hanlonr357 at gmail.com>
  • Date: Sat, 15 Feb 2014 23:14:17 -0500 (EST)
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  • References: <20140215090214.8888569D4@smc.vnet.net>

It is sometimes better to simplify expressions prior to using numerical
techniques.


$Version


"9.0 for Mac OS X x86 (64-bit) (January 24, 2013)"


Off[Floor::meprec] (* Supressing error messages. This does not change the
results. *)


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


2.


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


2.


Oddly, using PowerExpand results in an integer result despite the use of N


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


2


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


2



Bob Hanlon




On Sat, Feb 15, 2014 at 4:02 AM, psycho_dad <s.nesseris at gmail.com> wrote:

> Hi,
>
> 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
>
> Floor::meprec: Internal precision limit $MaxExtraPrecision = 50.` reached
> while evaluating Floor[Log[100]/Log[10]]. >>
>
> 1
>
> I'm on Math 9.0 + Win7, but Math 8 gives the same (wrong) result as well.
>
> Cheers
>
>




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