Re: Possible bug in Floor function?
- To: mathgroup at smc.vnet.net
- Subject: [mg132348] Re: Possible bug in Floor function?
- From: Matthias Bode <lvsaba at hotmail.com>
- Date: Sat, 15 Feb 2014 23:14:37 -0500 (EST)
- Delivered-to: l-mathgroup@mail-archive0.wolfram.com
- Delivered-to: l-mathgroup@wolfram.com
- Delivered-to: mathgroup-outx@smc.vnet.net
- Delivered-to: mathgroup-newsendx@smc.vnet.net
- References: <20140215090214.8888569D4@smc.vnet.net>
Hola, the "salient point": In[1]:= Log[1000, 1000000] Floor[Log[1000., x]] /. x -> 1000000 N[Floor[Log[1000., x]] /. x -> 1000000] N[Floor[Log[1000, x]] /. x -> 1000000] Floor[Log[1000, x]] /. x -> 1000000 Out[1]= 2 Out[2]= 2 Out[3]= 2. During evaluation of In[1]:= Floor::meprec:Internal precision limit $MaxExtraPrecision = 50.` reached while evaluating Floor[Log[1000000]/Log[1000]]. >> Out[4]= 2 During evaluation of In[1]:= Floor::meprec:Internal precision limit $MaxExtraPrecision = 50.` reached while evaluating Floor[Log[1000000]/Log[1000]]. >> Out[5]= Floor[Log[1000000]/Log[1000]] But not reliably so: In[1]:= Log[100, 10000] Floor[Log[100., x]] /. x -> 10000 N[Floor[Log[100., x]] /. x -> 10000] N[Floor[Log[100, x]] /. x -> 10000] Floor[Log[100, x]] /. x -> 10000 Out[1]= 2 Out[2]= 1 Out[3]= 1. During evaluation of In[1]:= Floor::meprec:Internal precision limit $MaxExtraPrecision = 50.` reached while evaluating Floor[Log[10000]/Log[100]]. >> Out[4]= 1 During evaluation of In[1]:= Floor::meprec:Internal precision limit $MaxExtraPrecision = 50.` reached while evaluating Floor[Log[10000]/Log[100]]. >> Out[5]= Floor[Log[10000]/Log[100]] In[7]:= $Version Out[7]= "9.0 for Microsoft Windows (64-bit) (January 25, 2013)" Best regards, MATTHIAS BODE. S 17.36398 W 66.218162'590 m. AMSL. > From: s.nesseris at gmail.com > Subject: Possible bug in Floor function? > To: mathgroup at smc.vnet.net > Date: Sat, 15 Feb 2014 04:02:14 -0500 > > 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 >
- References:
- Possible bug in Floor function?
- From: psycho_dad <s.nesseris@gmail.com>
- Possible bug in Floor function?