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Re: simple array math question [message #33687 is a reply to message #33685]

Fri, 17 January 2003 16:51

Heinz Stege
Messages: 189
Registered: January 2003

Senior Member

On Fri, 17 Jan 2003 16:10:49 -0600, "Sean Raffuse" <sean@me.wustl.edu>
wrote:

>
> "JD Smith" <jdsmith@as.arizona.edu> wrote in message
> news:pan.2003.01.17.21.46.58.749790.29842@as.arizona.edu...
>> On Thu, 16 Jan 2003 20:47:46 -0700, Craig Markwardt wrote:
>>
>>
>>> Heinz Stege <reply_to_posting@arcor.de> writes:
>>>> On Thu, 16 Jan 2003 14:05:27 -0600, "Sean Raffuse" <sean@me.wustl.edu>
>>>> wrote:
>>>>
>>>> >>> a=[[1,2,3],[4,5,6],[7,8,9]]
>>>> >
>>>> >>> b=[1,2,3]
>>>> >
>>>> >What is the best (read, fastest) way to multiply b by each individual
>>>> >row of a? I would like to return a result of:
>>>> >
>>>> >[[1,4,9],[4,10,18],[7,14,27]]
>>>>
>>>>
>>>> result=a*b(*,intarr(3))
>>>
>>> WOW! I've never seen that! It scares me how cool that is. :-)
>>>
>>> Craig
>>
>>
>> I may have to add that to the REBIN/REFORM tutorial. I'll see how fast
>> it is first. It's definitely one of the more readeable ways to add a new
>> trailing dimension. Doesn't work for leading or in-the-middle
>> dimensions, as far as I can tell.
>>
>> JD
>
> Yes, it worked wonders for me. Plenty fast compared to what I was doing
> before. I did have to use it on some leading dimensions and so am using
> transpose(). Not sure if it is the optimal solution, but good enough for my
> needs.
>

Yes, TRANSPOSE is also my favorite for the leading dimension:
result=a*(transpose(b))(intarr(3),*)

may be, you would prefer following syntax:
temp=transpose(b)
result=a*temp(intarr(3),*)

For middle dimensions REFORM does a good job :
c=fltarr(2,3,4)
...
d=fltarr(2,4)
...
result=c*(reform(d,2,1,4))(*,intarr(3),*)

(all tested with PV-Wave)

Heinz

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[Message index]

		Re: simple array math question By: marc schellens[1] on Sun, 19 January 2003 22:55
		Re: simple array math question By: Jeff Guerber on Fri, 17 January 2003 20:21
		Re: simple array math question By: Heinz Stege on Fri, 17 January 2003 16:51
		Re: simple array math question By: Sean Raffuse on Fri, 17 January 2003 14:10
		Re: simple array math question By: JD Smith on Fri, 17 January 2003 13:46
		Re: simple array math question By: Craig Markwardt on Thu, 16 January 2003 19:47
		Re: simple array math question By: Heinz Stege on Thu, 16 January 2003 16:26
		Re: simple array math question By: Craig Markwardt on Thu, 16 January 2003 13:30
		Re: simple array math question By: Pepijn Kenter on Fri, 24 January 2003 04:43
		Re: simple array math question By: JD Smith on Thu, 23 January 2003 08:53
		Re: simple array math question By: Heinz Stege on Sun, 26 January 2003 11:25
		Re: simple array math question By: Jeff Guerber on Sat, 25 January 2003 01:12

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