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Re: JULDAY-CALDAT problem [message #38239 is a reply to message #38233]

Fri, 27 February 2004 08:06

Paul Van Delst[1]
Messages: 1157
Registered: April 2002

Senior Member

Luciano wrote:
>
> Thanks David and Ben for your help. I've solved the problem by not
> using Julday and Caldat...
> David, if for the computer 0=10^-5 then is not me who has to start
> counting like a computer, it should be the other way around :)
>
> This is simply wrong and should be fixed at some level! I understand
> all the hardware, 0s and 1s, significant figures and related problems
> described in your "Help! The Sky is Falling!" section. But... don't
> you think this should be fixed somehow?
>
> If you ask me, 0 should be 0, and the computer should be able to know
> it...

0 is 0 on a computer. A number like 0.0 can, typically, be represented exactly. Same goes
for numbers like 1.0 or 2.0. When you start using 0.1's or 3.1415927's things get sticky.
And, when you start repeatedly adding and subtracting the sticky numbers that *can't* be
represented exactly, then the numeric precision issues crop up.

Having said all that, I hear you. It would be nice if the way we thought about these sorts
of problems was also how a computer handles them. When confronted with this sort of
situation, e.g. "the computer should be able to know", I just remember that a computer has
zero (exactly :o) intelligence. All the know-how and mistakes come from us.

cheers,

paulv

--
Paul van Delst
CIMSS @ NOAA/NCEP/EMC

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[Message index]

		Re: JULDAY-CALDAT problem By: James Kuyper on Fri, 27 February 2004 08:17
		Re: JULDAY-CALDAT problem By: Paul Van Delst[1] on Fri, 27 February 2004 08:06
		Re: JULDAY-CALDAT problem By: David Fanning on Fri, 27 February 2004 05:28
		Re: JULDAY-CALDAT problem By: lucianor on Fri, 27 February 2004 02:30
		Re: JULDAY-CALDAT problem By: David Fanning on Thu, 26 February 2004 08:51
		Re: JULDAY-CALDAT problem By: David Fanning on Thu, 26 February 2004 08:41
		Re: JULDAY-CALDAT problem By: btupper on Thu, 26 February 2004 08:17
		Re: JULDAY-CALDAT problem By: David Fanning on Thu, 26 February 2004 07:22
		Re: JULDAY-CALDAT problem By: btupper on Thu, 26 February 2004 06:52
		Re: JULDAY-CALDAT problem By: David Fanning on Thu, 26 February 2004 06:19
		Re: JULDAY-CALDAT problem By: Mark Hadfield on Sun, 29 February 2004 14:50

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