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Re: [Q]: ID analog to FORTRAN "sign" function [message #22001 is a reply to message #21932]

Thu, 12 October 2000 00:00

Dick Jackson
Messages: 347
Registered: August 1998

Senior Member

"Mark Hadfield" <m.hadfield@niwa.cri.nz> wrote in message
news:971127957.784431@clam-ext...
> "Alex Schuster" <alex@pet.mpin-koeln.mpg.de> wrote in message
> news:39E1C067.16F7488E@pet.mpin-koeln.mpg.de...
>> Rostyslav Pavlichenko wrote:
>>
>>> Does the IDl have something close to Fortran SIGN (DSIGN... so on...)
>>> functions
>>> ...
>>> result = SIGN (a, b)
>>> a (Input) Must be of type integer or real.
>>>
>>> b Must have the same type and kind parameters as a.
>>>
>>> Results:
>>> =========
>>> The result type is the same as a.
>>> The value of the result is
>>> | a | if b >= zero
>>> and -| a | if b < zero.
>>> ...
>> No, but you can easily write it:
>>
>> function sign, a, b
>> if ( b ge 0 ) then $
>> return, abs( a ) $
>> else $
>> return, -abs( a )
>> end
>
> The following is more compact and works when b is an array
>
> return, abs(a) * (fix(b ge 0) - fix(b lt 0))

Do I dare offer one more? Subscript lookups seem faster than arithmetic
operations, making this one faster, more compact and no less cryptic! :-)

Return, Abs(a) * ([-1, 1])[b GE 0]

A bit faster still, if you know the expected type of a and b, to avoid an
extra type conversion:

Return, Abs(a) * ([-1.0, 1.0])[b GE 0]

or

Return, Abs(a) * ([-1.0D, 1.0D])[b GE 0]

Cheers,
--
-Dick

Dick Jackson / dick@d-jackson.com
D-Jackson Software Consulting / http://www.d-jackson.com
Calgary, Alberta, Canada / Voice/Fax: +1-403-242-7398

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[Message index]

		[Q]: ID analog to FORTRAN "sign" function By: Rostyslav Pavlichenko on Fri, 06 October 2000 22:34
		Re: [Q]: ID analog to FORTRAN "sign" function By: Mark Hadfield on Thu, 12 October 2000 13:50
		Re: [Q]: ID analog to FORTRAN "sign" function By: Phillip David on Thu, 12 October 2000 00:00
		Re: [Q]: ID analog to FORTRAN "sign" function By: Dick Jackson on Thu, 12 October 2000 00:00
		Re: [Q]: ID analog to FORTRAN "sign" function By: Mark Hadfield on Mon, 09 October 2000 14:45
		Re: [Q]: ID analog to FORTRAN "sign" function By: Dick Jackson on Fri, 13 October 2000 00:00

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