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Re: Re: Unexpected behavior of Floor and IntegerPart

• To: mathgroup at smc.vnet.net
• Subject: [mg97939] Re: [mg97903] Re: Unexpected behavior of Floor and IntegerPart
• From: DrMajorBob <btreat1 at austin.rr.com>
• Date: Thu, 26 Mar 2009 05:21:06 -0500 (EST)
• References: <gqacr4$jbm$1@smc.vnet.net> <200903251043.FAA24548@smc.vnet.net>
• Reply-to: drmajorbob at bigfoot.com

Actually, 0.29*100 is internally represented in binary:

RealDigits[0.29*100, 2]

{{1, 1, 1, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
   1, 1, 1, 1, 1, 1, 1, 1}, 5}

Bobby

On Wed, 25 Mar 2009 05:43:45 -0500, Sjoerd C. de Vries  
<sjoerd.c.devries at gmail.com> wrote:

> 0.29*100 is internally represented as 28.999999999999996`. IntegerPart
> makes it 28 as it should.
>
> If you write IntegerPart[0.29`5*100] you get 29.
>
> Cheers -- Sjoerd
>
>
> On Mar 24, 12:32 pm, Curtis Osterhoudt <c... at lanl.gov> wrote:
>> Dear List,
>>
>>    I'm sure this is a result of non-infinite-precision arithmetic, bu=
> t it would be nice to have a more consistent behavior:
>>
>> In[26]:= IntegerPart[0.29*100]
>>
>> Out[26]= 28
>>
>> In[25]:= Floor[0.29*100]
>>
>> Out[25]= 28
>>
>> In[27]:= Floor[(29/100)*100]
>>
>> Out[27]= 29
>>
>> In[32]:= (Floor[#1*100] & ) /@ Range[0, 1, 0.01]
>>
>> Out[32]= {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, \
>> 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 28, 30, 31, 32, 33, \
>> 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, \
>> 51, 52, 53, 54, 55, 56, 57, 57, 59, 60, 61, 62, 63, 64, 65, 66, 67,
>> 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, \
>> 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100}
>>
>> In[33]:= Differences[%]
>>
>> Out[33]= {1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, \
>> 1, 1, 1, 1, 1, 1, 1, 1, 0, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, \
>> 1,
>>    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 2, 1, 1, 1, 1, 1, 1, 1, =
> \
>> 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
>>    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1}
>>
>> An interesting hint as to what may be happening is obtained by:
>>
>> ListPlot[Differences[(Floor[#1*100] & ) /@ Range[0, 100, 0.01]]]
>>
>>                      Regards,
>>                                     C=
> .O.
>>
>> --
>> =========================
> ==========================
> =========
>> Curtis Osterhoudt
>> cfo at remove_this.lanl.and_this.gov
>> PGP Key ID: 0x4DCA2A10
>> Please avoid sending me Word or PowerPoint attachments
>> Seehttp://www.gnu.org/philosophy/no-word-attachments.html
>> =========================
> ==========================
> =========
>
>



-- 
DrMajorBob at bigfoot.com

• References:
  • Re: Unexpected behavior of Floor and IntegerPart
    • From: "Sjoerd C. de Vries" <sjoerd.c.devries@gmail.com>