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Re: scalar system variable as single element array [message #80172 is a reply to message #80166]

Sun, 13 May 2012 16:58

lecacheux.alain
Messages: 325
Registered: January 2008

Senior Member

On 13 mai, 22:00, fawltylangu...@gmail.com wrote:
> Hi guys,
>
> the IDL help says that a scalar can be considered a single element array. So why is the following expression failing?
>
> IDL> help, !pi[0]
> % Expression must be an array in this context: !PI.
> % Execution halted at: $MAIN$
>
> Is it a bug or feature :-)
>
> regards,
> Lajos
>
>

Because, in IDL, as far as I know, scalar and array are two different
things!
!pi is not an array, but [!pi] is. If a scalar could be considered as
a single element array, the IDL implicit dimension rule would fail:
IDL> help,indgen(10) + !pi
<Expression> FLOAT = Array[10]
IDL> help,indgen(10) + [!pi]
<Expression> FLOAT = Array[1]
Conversely, a single element array cannot be considered as a scalar,
unless you explicitely address it:
IDL> help,indgen(10) + ([!pi])[0]
<Expression> FLOAT = Array[10]
Cheers,
alx.

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[Message index]

		Re: scalar system variable as single element array By: Mats Löfdahl on Sun, 13 May 2012 23:31
		Re: scalar system variable as single element array By: Lajos Foldy on Sun, 13 May 2012 23:23
		Re: scalar system variable as single element array By: lecacheux.alain on Sun, 13 May 2012 16:58

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