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Sky Falling, etc. : Array substitution + addition with plus-equal (+=) [message #52941]

Mon, 12 March 2007 14:17

MarioIncandenza
Messages: 231
Registered: February 2005

Senior Member

Tentatively filed under "The Sky Is Falling!," and I hope it will be
resolved in the same fashion.

Here is the test case, which gives the correct result:

IDL> test=fltarr(2,2,4)
IDL> testadd=fltarr(2,2,2) + 1
IDL> print,total(test),total(testadd)
0.00000 8.00000
IDL> test[0,0,1] += testadd
IDL> print,total(test),total(testadd)
8.00000 8.00000
IDL> test[0,0,1] += testadd
IDL> print,total(test),total(testadd)
16.0000 8.00000
IDL> print,test
0.00000 0.00000
0.00000 0.00000

2.00000 2.00000
2.00000 2.00000

2.00000 2.00000
2.00000 2.00000

0.00000 0.00000
0.00000 0.00000

That is exactly what I expect from this operation.

Here is another case, with results somewhat different
IDL> test=fltarr(2,2,4)
IDL> testadd=fltarr(2,2,2)
IDL> testadd[0,0,*]=1
IDL> print,total(test),total(testadd)
0.00000 2.00000
IDL> test[0,0,1] += testadd
IDL> print,total(test),total(testadd)
2.00000 2.00000
IDL> print,test
0.00000 0.00000
0.00000 0.00000

1.00000 0.00000
0.00000 0.00000

1.00000 0.00000
0.00000 0.00000

0.00000 0.00000
0.00000 0.00000 ; So far, so good
IDL> test[0,0,1] += testadd ; Now, let's add again
IDL> print,total(test),total(testadd)
10.0000 2.00000 ; Pardon the
expression, WTF?
IDL> print,test
0.00000 0.00000
0.00000 0.00000

2.00000 1.00000
1.00000 1.00000

2.00000 1.00000
1.00000 1.00000

0.00000 0.00000
0.00000 0.00000 ; Not even JD Smith
expected _that_.

Any ideas?

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[Message index]

		Sky Falling, etc. : Array substitution + addition with plus-equal (+=) By: MarioIncandenza on Mon, 12 March 2007 14:17
		Re: Sky Falling, etc. : Array substitution + addition with plus-equal (+=) By: JD Smith on Tue, 13 March 2007 13:37
		Re: Sky Falling, etc. : Array substitution + addition with plus-equal (+=) By: MarioIncandenza on Tue, 13 March 2007 11:35
		Re: Sky Falling, etc. : Array substitution + addition with plus-equal (+=) By: JD Smith on Tue, 13 March 2007 10:46
		Re: Sky Falling, etc. : Array substitution + addition with plus-equal (+=) By: Foldy Lajos on Tue, 13 March 2007 05:26
		Re: Sky Falling, etc. : Array substitution + addition with plus-equal (+=) By: Y.T. on Tue, 13 March 2007 00:19

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