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Re: Check if coordinate is in array [message #34192 is a reply to message #34072]

Thu, 20 February 2003 14:30

condor
Messages: 35
Registered: January 2002

Member

Thomas Gutzler <tgutzler@ee.uwa.edu.au> wrote in message news:<3E544CAB.6020006@ee.uwa.edu.au>...
> Hi again.
>
> Here is the daily riddle:
> Is there a faster way to check, if a coordinate (2-element array) is
> element of an array of coordinates (2,n-element array) than this:
>
> FUNCTION is_element_of_2D, x, arr
> xidx = WHERE(arr[0,*] EQ x[0], c1)
> yidx = WHERE(arr[1,*] EQ x[1], c2)
> IF (c1 + c2 GT 0) THEN tmp = WHERE(MATRIX_MULTIPLY(xidx, $
> 1./TRANSPOSE(yidx)) EQ 1, c3) ELSE c3 = 0
> RETURN, c3 NE 0
> END
>
> Example:
> arr = [[1,2], [3,4], [3,2]]
> x = [3,4]
> y = [2,3]
> print, is_element_of_2D(x, arr)
> print, is_element_of_2D(y, arr)
>
> Tom

I don't know the context of this snippet of code, but in my math
background there is the strong notion that all plane geometry should
always be done in complex numbers as you get the whole world of
Wirtinger calculus for free.

In IDL you get this:

IDL> help,f,g
F COMPLEX = ( 1.00000, 2.00000)
G COMPLEX = Array[4]
IDL> print,g,format='(10(2i2,3x))'
3 4 8 3 1 2 4 5
IDL> print,where(g eq f)
2

So if you could keep your coordinates in complex variables from the
beginning, you can match them and compare them to each other and
such...

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[Message index]

		Check if coordinate is in array By: Thomas Gutzler on Wed, 19 February 2003 19:34
		Re: Check if coordinate is in array By: condor on Thu, 20 February 2003 14:30
		Re: Check if coordinate is in array By: Chris[1] on Thu, 20 February 2003 06:36

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