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Re: Possreps and numeric types

From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Thu, 29 Mar 2007 20:36:39 GMT
Message-ID: <rrVOh.17061$PV3.175756@ursa-nb00s0.nbnet.nb.ca>


Gene Wirchenko wrote:
> Bob Badour <bbadour_at_pei.sympatico.ca> wrote:
>
>

>>Gene Wirchenko wrote:
>>
>>
>>>Bob Badour <bbadour_at_pei.sympatico.ca> wrote:
>>>
>>>
>>>>Gene Wirchenko wrote:
>>>>
>>>>
>>>>>Bob Badour <bbadour_at_pei.sympatico.ca> wrote:
>>>>>
>>>>>
>>>>>>Gene Wirchenko wrote:
>>>>>>
>>>>>>
>>>>>>>Bob Badour <bbadour_at_pei.sympatico.ca> wrote:
>>>>>>>
>>>>>>>[snip]
>>>>>>>
>>>>>>>
>>>>>>>>I admit I used epsilon somewhat sloppily and not necessarily with the 
>>>>>>>>exact meaning used when discussing a particular floating-point 
>>>>>>>>implementation. I used it to mean the distance to the representable 

>
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
>>>>>>>>predecessor or successor of any representable rational value.

>
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
>>>>>>>   That is incorrect.  It is per
>>>>>>>        http://en.wikipedia.org/wiki/Machine_epsilon
>>>>>>>In a floating-point system, epsilon is the smallest number such that

>
> ^^^^^^^^^^^^^^^^^^^^^^^^^
>
>>>>>>> 1 + epsilon > 1
>
> ^^^^^^^^^^^^^^^
>
>>>>>>>[snip]
>>>>>>
>>>>>>When you say the above is incorrect, are you saying I was not using 
>>>>>>epsilon sloppily? Or are you saying I didn't use it to mean the distance 
>>>>>>to the representable predecessor or successor of any representable 
>>>>>>rational value?
>>>>>
>>>>>    The definition of epsilon.
>>>>
>>>>Other than the "scaled by the exponent" bit, what exactly is the 
>>>>difference? ie. If I subtracted one from the other, what answer would I get?
>>>
>>>     If I am understanding you, other than that difference, none.  The
>>>answer would be garbage.
>>
>>I really don't understand your objection. I noted I used the term 
>>sloppily and not as defined for floating point when I was discussing 
>>rational representations. Using the only definition I gave for the 
>>floating point version, the difference would be zero. The definitions 
>>are equivalent only stated differently.

>
> No. The definition that I gave is in terms of 1, not just any
> representatable value.

I guess I will just roll my eyes and move along. Received on Thu Mar 29 2007 - 15:36:39 CDT

Original text of this message

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