Re: Math Error?

[Norman Palardy <npalardy at great-white-software dot com>]

On Jul 28, 2006, at 8:53 AM, Peter K. Stys wrote:

> In[26]:= N[72/2000*750,100]
>
> Out[26]=  
> 27.0000000000000000000000000000000000000000000000000000000000000000000 
> 0000000000000000000000000000000
> In[27]:= N[72/2000*750]
>
> Out[27]= 27.
>
> Still suggests all these numbers and intermediate results are
> representable exactly at machine precision.
I'm quite certain that 72/2000 is not.
Write it as the simple sum of powers of 2 and you find the problem.
72/2000 = 2^-2 + 2^-4 + 2^-5 + 2^-6 + 2^-11 + 2^-15 ..... and so on  
and you never get exactly the result you get from 72/2000.
In the machine all you have is powers of 2


_______________________________________________
Unsubscribe or switch delivery mode:
<http://www.realsoftware.com/support/listmanager/>

Search the archives of this list here:
<http://support.realsoftware.com/listarchives/lists.html>