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Re: a bug in RealDigits? Mathematica 5.0

• To: mathgroup at smc.vnet.net
• Subject: [mg45219] Re: [mg45211] a bug in RealDigits? Mathematica 5.0
• From: Murray Eisenberg <murray at math.umass.edu>
• Date: Sun, 21 Dec 2003 03:42:13 -0500 (EST)
• Organization: Mathematics & Statistics, Univ. of Mass./Amherst
• References: <200312201056.FAA09603@smc.vnet.net>
• Reply-to: murray at math.umass.edu
• Sender: owner-wri-mathgroup at wolfram.com

It looks like a simple matter of loss of precision:


   t1 = 39383738378094852309445543850343.49494;
   Precision[t1]
36.5953

You need to specify you want greater precision, presumably the full 37 
digits:


   t2 = 39383738378094852309445543850343.49494`37
   Precision[t2]
37.
   First @ RealDigits[t2]
{3, 9, 3, 8, 3, 7, 3, 8, 3, 7, 8, 0, 9, 4, 8, 5, 2, 3, 0, 9, 4, 4, 5, \
5, 4, 3, 8, 5, 0, 3, 4, 3, 4, 9, 4, 9, 4}

You may accomplish the same thing with:

   t2 = SetPrecision[39383738378094852309445543850343.49494, 37]

steve_H wrote:

> hello;
> 
> Mathematica 5.0, student version, on XP home edition:
> 
> t1 = 39383738378094852309445543850343.49494
>  
> {c, d} = RealDigits[t1];
> 
> now c is 
> 
> {3, 9, 3, 8, 3, 7, 3, 8, 3, 7, 8, 0, 9, 4, 8, 5, 2, 3, 0, 9, 
> 4, 4, 5, 5, 4, 3, 8, 5, 0, 3, 4, 3, 4, 9, 4, 9}
> 
> notice that I typed in the last digits of t1 as '.49494', i.e the
> number to the right of the decimal point.
> 
> But 'c' above is missing the last digit, it only reports '4,9,4,9' 
> instead of '4,9,4,9,4'
> 
> What happened to the last digit '4' ?
> 
> 

-- 
Murray Eisenberg                     murray at math.umass.edu
Mathematics & Statistics Dept.
Lederle Graduate Research Tower      phone 413 549-1020 (H)
University of Massachusetts                413 545-2859 (W)
710 North Pleasant Street            fax   413 545-1801
Amherst, MA 01003-9305

• References:
  • a bug in RealDigits? Mathematica 5.0
    • From: nma124@hotmail.com (steve_H)