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MathGroup Archive 2007

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Re: MachinePrecission and FPU

  • To: mathgroup at smc.vnet.net
  • Subject: [mg81292] Re: MachinePrecission and FPU
  • From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
  • Date: Tue, 18 Sep 2007 05:55:15 -0400 (EDT)
  • Organization: The Open University, Milton Keynes, UK
  • References: <fcnl4n$s65$1@smc.vnet.net>

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,
-- 
Jean-Marc


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