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Re: lower and upper triangular matrices [message #84366 is a reply to message #84365]

Thu, 30 May 2013 03:51

Mats Löfdahl
Messages: 263
Registered: January 2012

Senior Member

Den torsdagen den 30:e maj 2013 kl. 12:05:16 UTC+2 skrev fd_...@mail.com:
> On Thursday, 30 May 2013 02:33:48 UTC+1, Craig Markwardt wrote:
>
>> What do you mean? Do you want to factor a matrix, such as with CHOLDC? Or do you just want to extract the upper and lower triangle elements from a matrix?
>
> I need the upper and lower triangle elements from a matrix. I am trying to use the Gauss-Seidel method.

Like this?

IDL> n=4
IDL> a=indgen(n,n)+1
IDL> ii=indgen(n) # replicate(1,n)
IDL> jj=indgen(n) ## replicate(1,n)
IDL> print,a
1 2 3 4
5 6 7 8
9 10 11 12
13 14 15 16
IDL> print,a*(ii lt jj)
0 0 0 0
5 0 0 0
9 10 0 0
13 14 15 0
IDL> print,a*(ii ge jj)
1 2 3 4
0 6 7 8
0 0 11 12
0 0 0 16

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[Message index]

		Re: lower and upper triangular matrices By: fd_luni on Thu, 30 May 2013 03:56
		Re: lower and upper triangular matrices By: Mats Löfdahl on Thu, 30 May 2013 03:51
		Re: lower and upper triangular matrices By: fd_luni on Thu, 30 May 2013 03:05
		Re: lower and upper triangular matrices By: Craig Markwardt on Wed, 29 May 2013 18:33
		Re: lower and upper triangular matrices By: fd_luni on Thu, 30 May 2013 03:55

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