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Re: Weird MIN behavior [message #42745 is a reply to message #42743]

Sun, 20 February 2005 14:42

Mark Hadfield
Messages: 783
Registered: May 1995

Senior Member

Michael Wallace wrote:
> Can someone explain this?
>
>
> Normal case; everything works as you expect.
>
> IDL> a = [1.0, 2.0, 3.0, 4.0, 5.0]
> IDL> b = min(a, MAX = c)
> IDL> print, b, c
> 1.00000 5.00000
>
>
> Abnormal case; why doesn't this work?
>
> IDL> a = [1.0, 2.0, 3.0, 4.0, 5.0]
> IDL> r = dblarr(2)
> IDL> r[0] = min(a, MAX = r[1])
> % MIN: Expression must be named variable in this context: <DOUBLE ((
> 0.00000, 0.00000))>.

It's complaining about the argument passed to the MAX keyword. As it
says, this must be a named variable, and a subscripted variable does not
qualify because it is passed by value. You're lucky that IDL tells you
that it doesn't accept a subscripted variable here--in other situations
it quitely leaves the value unmodified and let's you puzzle it out later.

See IDL documentation on "Parameter Passing Mechanism". Also David
Fanning's site has relevant material, eg see the info about the correct
use of the ARG_PRESENT function in

http://www.dfanning.com/tips/keyword_check.html

and also

http://www.dfanning.com/tips/read_subscripted_array.html

--
Mark Hadfield "Ka puwaha te tai nei, Hoea tatou"
m.hadfield@niwa.co.nz
National Institute for Water and Atmospheric Research (NIWA)

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[Message index]

		Re: Weird MIN behavior By: David Fanning on Mon, 21 February 2005 16:56
		Re: Weird MIN behavior By: Michael Wallace on Mon, 21 February 2005 16:49
		Re: Weird MIN behavior By: James Kuyper on Mon, 21 February 2005 16:13
		Re: Weird MIN behavior By: Michael Wallace on Sun, 20 February 2005 17:56
		Re: Weird MIN behavior By: David Fanning on Sun, 20 February 2005 17:31
		Re: Weird MIN behavior By: Michael Wallace on Sun, 20 February 2005 17:12
		Re: Weird MIN behavior By: Mark Hadfield on Sun, 20 February 2005 14:42
		Re: Weird MIN behavior By: David G. Grier on Sun, 20 February 2005 14:28

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