Hi all
I'm glad someone has finally (specifically) mentioned the issue of
declared data precision (including parameters) !
(One must presume, of course, that all the learned persons on this list
have this fact firmly in mind when porting.)
Kind regards to all
Gaz
-----Original Message-----
From: David Hitchin [mailto:[log in to unmask]]
Sent: Wednesday, 17 October 2001 23:24
To: [log in to unmask]
Subject: Re: 128 bits of precision?
> On Wed, 17 Oct 2001, Popa, Frank D. asked
>
>> I'm curious as to who would need 128 bits of precision?
>
> I often need more than 64 bits. A typical example is with
> expressions like (1.D0 - A). If A = 0.99999999912D0 (14 significant
> figures), 1 - A is 8.8D-10, with only 2 significant figures.
> Small differences of two large numbers occur frequently,
> especially if the numbers are squares (calculations of
> variance) or in the resolution of ill-determined systems of
> equations. As a matter of fact, I am a bit surprised to see
> such a question asked by somebody who "did iterative solutions of
large
> matrices".
>
There are situations, such as in number theory, in which the data values
are known precisely or to a very high degree of precision. However, very
few physical measurements have more than 7 significant figures. In any
particular application it is important to consider whether the errors in
computed results are dominated by lack of precision in the computation,
or
lack of precision in the data.
David Hitchin
************************************************************************
The information in this e-mail together with any attachments is
intended only for the person or entity to which it is addressed
and may contain confidential and/or privileged material.
Any form of review, disclosure, modification, distribution
and/or publication of this e-mail message is prohibited.
If you have received this message in error, you are asked to
inform the sender as quickly as possible and delete this message
and any copies of this message from your computer and/or your
computer system network.
************************************************************************
|