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Re: Serious Bug in Mathematica 7 and 8.0.4.0 (latest version)

• To: mathgroup at smc.vnet.net
• Subject: [mg126190] Re: Serious Bug in Mathematica 7 and 8.0.4.0 (latest version)
• From: Christoph Lhotka <christoph.lhotka at fundp.ac.be>
• Date: Tue, 24 Apr 2012 05:32:33 -0400 (EDT)
• Delivered-to: l-mathgroup@mail-archive0.wolfram.com
• References: <201204230941.FAA16597@smc.vnet.net>

hi,

it is not a bug.

SetPrecision adds 0 in base 2 which are not necessarily 0's in base 10 
(see documentation).


Advice: Don't use SetPrecision if you want to specify that a number is 
of given precision.

Use the notation X`NN where X is the number and NN is the precision.


In[]:= b = 6371.01`20

Out[]:=  6371.0100000000000000


In[]:=Precision[b]

  Out[]:.


Best,

Christoph


On 04/23/2012 11:41 AM, Alexander Mayer wrote:
> In[1]:= (* This notebook produced by Mathematica 8.0.4.0 *)
> (* Platform: OSX 10.6.8 on MacBook Pro *)
>
> In[1]:= b = 6371.01 (* We set the value of b to this real number. *)
>
> Out[1]= 6371.01
>
> In[2]:= SetPrecision[a = b, 20] (* We test the actual value of b. *)
>
> Out[2]= 6371.0100000000002183
>
> In[3]:= (* Mathematica has added a small constant! *)
>
> In[4]:= (* Adding zeros to the 16th place fixes the problem. *)
>
> In[5]:= c = 6371.0100000000000000
>
> Out[5]= 6371.0100000000000000
>
> In[6]:= SetPrecision[a = c, 20]
>
> Out[6]= 6371.0100000000000000
>

• References:
  • Serious Bug in Mathematica 7 and 8.0.4.0 (latest version)
    • From: Alexander Mayer <amayer@alum.mit.edu>