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Re: Patch to userlib/deriv.pro to add MAX_VALUE keyword [message #1556 is a reply to message #1554]

Mon, 27 December 1993 08:04

thompson
Messages: 584
Registered: August 1991

Senior Member

rfinch@water.ca.gov (Ralph Finch) writes:

> Following context diff, when run through patch, will add the MAX_VALUE
> keyword to the userlib function deriv.pro. However, I still believe
> it would be better if IDL had the fundamental notion of missing values
> built-in to their basic mathematics; IEEE NaN might be a good choice.
> If IDL understood NaN's, you wouldn't even need keywords for missing
> values or max_value (presuming that most usage of MAX_VALUE really is
> for missing values).

However, not all computer platforms use the IEEE standard. A notable exception
is Digital's VAX platform, which represents a large proportion of IDL's
users--in fact IDL came out of the VAX/PDP world before it was ported to Unix,
etc. As far as I know, there's no equivalent concept to NaNs in the VAX
architecture.

Bill Thompson

P.S. Although Digital's Alpha workstations support both the VAX and IEEE
floating point standards, my understanding is that IDL uses the VAX floating
point representation, at least within OpenVMS, for backwards compatibility with
the VAX/VMS architecture. I'm not sure which is used in OSF/1, although it
would seem most advantageous to use the IEEE format for compatibility with
MIPS/Ultrix workstations. I'm also not certain whether there's a performance
tradeoff between using VAX and IEEE floating point numbers on the Alpha.

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[Message index]

		Re: Patch to userlib/deriv.pro to add MAX_VALUE keyword By: thompson on Mon, 27 December 1993 15:23
		Re: Patch to userlib/deriv.pro to add MAX_VALUE keyword By: nowicki on Mon, 27 December 1993 02:50
		Re: Patch to userlib/deriv.pro to add MAX_VALUE keyword By: schmitt on Mon, 27 December 1993 12:34
		Re: Patch to userlib/deriv.pro to add MAX_VALUE keyword By: thompson on Mon, 27 December 1993 08:04

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