| Re: Multiplication turning array into scalar -- who wants to try? [message #53256] |
Sun, 01 April 2007 00:13 |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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swingnut@gmail.com writes:
> Hooray for cross-posting! That's good to know. I guess now I'm just
> confused, because I've not encountered such a difference in the
> treatment of scalars and 1x1 arrays. This implies that a scalar is not
> an array to me despite the spiel about IDL being an array language, so
> that somewhere in its innards IDL treats a scalar and 1x1 array
> differently but doesn't always make the result apparent to the user
> unless said code monkey traces whatever went awry back to this
> difference of treatment.
Oh, oh. Don't even get started along this path, or it's
all we are going to talk about all week. IDL just is what
it is. :-(
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Sepore ma de ni thui. ("Perhaps thou speakest truth.")
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| Re: Multiplication turning array into scalar -- who wants to try? [message #53258 is a reply to message #53256] |
Sat, 31 March 2007 21:24  |
swingnut
Messages: 30
Registered: September 2005
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Member |
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On Apr 1, 12:01 am, David Fanning <n...@dfanning.com> wrote:
...
> Your "signOfDifference" is a one-element array. When you multiply
> an array by another array, the result has as many elements as
> the *smallest* array.
>
> Cheers,
>
> David
> --
> David Fanning, Ph.D.
> Fanning Software Consulting, Inc.
> Coyote's Guide to IDL Programming:http://www.dfanning.com/
> Sepore ma de ni thui. ("Perhaps thou speakest truth.")
Hooray for cross-posting! That's good to know. I guess now I'm just
confused, because I've not encountered such a difference in the
treatment of scalars and 1x1 arrays. This implies that a scalar is not
an array to me despite the spiel about IDL being an array language, so
that somewhere in its innards IDL treats a scalar and 1x1 array
differently but doesn't always make the result apparent to the user
unless said code monkey traces whatever went awry back to this
difference of treatment.
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| Re: Multiplication turning array into scalar -- who wants to try? [message #53260 is a reply to message #53258] |
Sat, 31 March 2007 22:01 |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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swingnut@gmail.com writes:
> JOURNALING AT IDL PROMPT:
>
> temp=[0.0,-1.0,0.0]
> print,size(temp)
> ; 1 3 4 3
> temp2=-25.0
> print,size(temp2)
> ; 0 4 1
> print,temp2/ABS(temp2)
> ; -1.00000
> temp2=temp2/ABS(temp2)
> print,SIZE(temp2)
> ; 0 4 1
> print,temp2*temp
> ; 0.000000 1.00000 0.000000
> temp=temp2*temp
> print,temp
> ; 0.000000 1.00000 0.000000
> print,SIZE(temp)
> ; 1 3 4 3
>
> OUTPUT OF SEQUENCE OF PRINT STATEMENTS IN MY CODE:
>
> ;----------
> ;Adjusting density power law in increments of [0.000000 , -1.00000 ,
> 0.000000 ]
> ;adjustmentIncrement =
> ; 0.000000 -1.00000 0.000000
> ;SIZE of adjustmentIncrement =
> ; 1 3 4 3
> ;-----
> ;deltaVirtHeight =
> ; -0.0678234
> ;SIZE of deltaVirtHeight =
> ; 1 1 4 1
> ;-----
> ;signOfDifference = deltaVirtHeight/ABS(deltaVirtHeight) =
> ; -1.00000
> ;SIZE of signOfDifference =
> ; 1 1 4 1
> ;-----
> ;Multiply signOfDifference with each element of adjustmentIncrement,
> i.e.,
> ;adjustmentIncrement[i]=adjustmentIncrement[i]*signOfDiffere nce,
> i=0,1,2:
> ;adjustmentIncrement =
> ; 0.000000 1.00000 0.000000
> ;SIZE of adjustmentIncrement =
> ; 1 3 4 3
> ;-----
> ;But if we do
> adjustmentIncrement=adjustmentIncrement*signOfDifference, it becomes a
> scalar?
> ;adjustmentIncrement =
> ; 0.000000
> ;SIZE of adjustmentIncrement =
> ; 1 1 4 1
> ; % Attempt to subscript LOCDENSPL with <INT ( 1)> is out
> of range.
It is a little hard to discern a question here, but
I think you are confusing yourself by using the SIZE
function. Using a HELP command might help more. Here
is what is happening:
IDL> a = [1,2,3]
IDL> b = [3]
IDL> print, a*b
3
IDL> print, size(b)
1 1 2 1
IDL> help, b
B INT = Array[1]
IDL> b = 3
IDL> print, a*b
3 6 9
IDL> help, b
B INT = 3
IDL> print, size(b)
0 2 1
Your "signOfDifference" is a one-element array. When you multiply
an array by another array, the result has as many elements as
the *smallest* array.
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Sepore ma de ni thui. ("Perhaps thou speakest truth.")
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