Re: User selectable lower array bound?

[Marcus O'Brien <m.obrien(at)sghms.ac.uk>]

Yep,

This is something I wanted to use for converting images to center of mass coordinates for
principle axes transformations, ended up faffing around to simulate it. The concept does
appear in display coordinate systems for objects though (well it seems vaguely related to
me).

Marc

Paul van Delst wrote:

> Hey there,
>
> Is is just me, or would anyone else find useful the ability to define arrays in IDL such
> that the lower bound is *not* always zero? Sorta like:
>
>   x = FINDGEN( 11, LOWER = -5 )
> or
>   y = DBLARR( 100, LOWER = 1 )
>
> so that accessing elements such as x[ -4 ] or y[ 100 ] are o.k.?
>
> I know this can be done now with judicious use of proxy indices, e.g.
>
>   FOR i = -5, 5 DO BEGIN
>     ix = i + 5
>     PRINT, x[ ix ]
>     ....do other stuff with negative i's....
>   ENDFOR
>
> but sometimes this makes code hard to follow (or explain to someone who's never used the
> code before) in direct correspondence with a physical process.
>
> It seems like such a simple thing to be able to do (with default action being start at
> index 0) although I'm sure the amount of work required to implement this would be
> horrendous. Still, it shur would be nice.....
>
> paulv
>
> --
> Paul van Delst           A little learning is a dangerous thing;
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