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Re: Array Multiplication [message #79657 is a reply to message #26191]

Sun, 25 March 2012 12:58

Craig Markwardt
Messages: 1869
Registered: November 1996

Senior Member

On Sunday, March 25, 2012 5:22:00 AM UTC-4, IDL beginner wrote:
> Dear All,
>
> I have the following question. Let's say we have a vector A and matrix
> array B so that:
>
> A = [1, 2, 5, 2, 3]
>
> B = [[2, 4], [1, 9]]
>
> I want to multiply each element of the vector A with the matrix array
> B but WITHOUT using a FOR loop. Is that possible??? I need to do so in
> order to save execution time.
>
> The output result should be an array C with dimensions C[2, 2, 5, 1].

C = intarr(2,2,5,1)
C[0,0,*,*] = B[0,0]*A
C[0,1,*,*] = B[0,1]*A
C[1,0,*,*] = B[1,0]*A
C[1,1,*,*] = B[1,1]*A

Since there are only four elements, there are no FOR loops needed.

I suppose that you are trying to frame a more generic problem. My recommendation is at first, don't worry about whether you are using FOR loops or not. Make each iteration of the loop do as much work as possible, and you should be fine.

Craig

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[Message index]

		Array multiplication: implicit loop query By: george on Fri, 10 August 2001 03:56
		Re: Array multiplication: implicit loop query By: bennetsc on Tue, 14 August 2001 23:57
		Re: Array multiplication: implicit loop query By: Richard Younger on Mon, 13 August 2001 13:59
		Re: Array multiplication: implicit loop query By: david[2] on Mon, 13 August 2001 11:52
		Re: Array multiplication: implicit loop query By: Richard Younger on Mon, 13 August 2001 11:37
		Re: Array multiplication: implicit loop query By: david[2] on Mon, 13 August 2001 07:55
		Re: Array multiplication: implicit loop query By: Craig Markwardt on Mon, 13 August 2001 06:58
		Re: Array multiplication: implicit loop query By: Paul van Delst on Mon, 13 August 2001 06:46
		Re: Array Multiplication By: Craig Markwardt on Sun, 25 March 2012 12:58
		Re: Array Multiplication By: lecacheux.alain on Sun, 25 March 2012 08:09

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