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MathGroup Archive 2007

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Re: MachinePrecission and FPU

  • To: mathgroup at smc.vnet.net
  • Subject: [mg81316] Re: MachinePrecission and FPU
  • From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
  • Date: Wed, 19 Sep 2007 05:24:31 -0400 (EDT)
  • Organization: The Open University, Milton Keynes, UK
  • References: <fcnl4n$s65$1@smc.vnet.net> <46EF98F4.8060601@gmail.com> <fco7i4$3sq$1@smc.vnet.net>

Daniel Huber wrote:
> Hy Jean-Marc,
> thank's for the response. Note that 0.03/0.006 gives you a rounded 
> number (OutputForm). If you want to see all digits you have to look at 
> the InputForm:
> 0.03/0.006 //InputForm
> it would be interessting to know if with this you may get a different 
> result.
> Daniel

I confirm that with ImputForm I get 4.9999... (I did not try the first 
time).

> Jean-Marc Gulliet wrote:
>> dh wrote:
>>
>>> I could trace down a discrepancy between a C program and Mathematica 
>>> to the
>>>
>>> following. Try to compute 0.03/0.006 and you get 4.9999999.. as neither
>>>
>>> 0.03 nor 0.006 can be represented accurately, this is not amazing.
>> On my system (Intel Pentium 4 HT 2.6 MHz), I get consistently 5.0 with 
>> version 6.0.1 and 5.2.
>>
>> In[1]:= 0.03/0.006
>>
>> Out[1]= 5.
>>
>> In[2]:= $Version
>>
>> Out[2]= "6.0 for Microsoft Windows (32-bit) (June 19, 2007)"
>>
>> In[1]:=
>> 0.03/0.006
>>
>> Out[1]=
>> 5.
>>
>> In[2]:=
>> $Version
>>
>> Out[2]=
>> 5.2 for Microsoft Windows (June 20, 2005)
>>
>>> However, the same calculated with C and C++ on PC's gives 5.0000..
>> /* Very crude C program */
>>
>> #include <stdio.h>
>>
>> int main(void)
>> {
>>     printf("The value of 0.03/0.006 is %f\n", 0.03/0.006);
>>
>>     return 0;
>> }
>>
>> which returns after compilation
>>
>> The value of 0.03/0.006 is 5.000000
>>
>>> Now, WHY?
>> Could that be hardware dependent? You did not mention either the 
>> version of Mathematica your used or the cpu.
>>
>> <snip>
>>
>> Regards,
> 



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