AW: floating Point reprsentation was perceived Calculation error in MS

[MikeSuesserott@xxxxxxxxxxx (MikeSuesserott)]

Hi David,

useful information on the IEEE floating-point standard (almost universally
used nowadays) can be found at
http://www.psc.edu/general/software/packages/ieee/ieee.html

Best regards,

Michael Suesserott


> -----Ursprungliche Nachricht-----
> Von: owner-metastock@xxxxxxxxxxxxx
> [mailto:owner-metastock@xxxxxxxxxxxxx]Im Auftrag von David Jennings
> Gesendet: Monday, October 01, 2001 19:22
> An: metastock@xxxxxxxxxxxxx
> Betreff: Re:floating Point reprsentation was perceived
> Calculation error in MS
>
>
> Sorry, but I long ago forgotten all that I ever knew about internal
> representation and floating point precision. I was trained as a scientist,
> so 'am very wary of mistaken views of precision. But, here's an example:
> I have a very large SQL server database of stock  and commodity
> prices which
> I use in testing. Now numbers from the exchange typically come in as say
> 49.25. I store them in the database as double prcision floating point.
> However, the number is very often not stored as 49.249999999999999..... or
> it's equivalent in floating point.
>
> I would urge you to read say, numerical recipes  by Press,
> Teukolsky et al,
> In this they talk about floating point representation, and the last bit
> being a phantom i.e., it could be turned on or off. e.g. a half- and I
> choose that form precisely, would be represented by 0 (the sign bit)
> followed by 01111111 the last bit could be a phantom 1 or zero. This is a
> function of machine accuracy. Clearly, one can use packages such as
> Mathematica with enhanced floating point represention but I
> believe that one
> should uunderstand what one is modelling, My advice is recognise that one
> will not always get precisely the effect one would expect and code
> accordingly. Are you going to do a deal when an indicator reads
> 2.00000000000 and not 2.0000000000001 or 1.99999999999999?
>