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Re: Matlab Syntax [message #37031 is a reply to message #37029]

Thu, 20 November 2003 12:38

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Folks,

I need more Matlab help. Here is the line I am
struggling with:

invAI = inv(A + gamma * diag(ones(1,N)));

A is a matrix and gamma is the scalar 1.0.

Here is the output from Matlab when I print
A and invAI:

A =
8 -5 1 1 -5
-5 8 -5 1 1
1 -5 8 -5 1
1 1 -5 8 -5
-5 1 1 -5 8

invAI =

0.3158 0.2105 0.1316 0.1316 0.2105
0.2105 0.3158 0.2105 0.1316 0.1316
0.1316 0.2105 0.3158 0.2105 0.1316
0.1316 0.1316 0.2105 0.3158 0.2105
0.2105 0.1316 0.1316 0.2105 0.3158

I have the matrix A in my IDL session:

IDL> print, array
8.00000 -5.00000 1.00000 1.00000 -5.00000
-5.00000 8.00000 -5.00000 1.00000 1.00000
1.00000 -5.00000 8.00000 -5.00000 1.00000
1.00000 1.00000 -5.00000 8.00000 -5.00000
-5.00000 1.00000 1.00000 -5.00000 8.00000

But I get the wrong answers when I invert. Here is
my translation of the Matlab inverse line:

invARRAY = Invert((ARRAY + gamma) ## Diag_Matrix(Replicate(1,npts)) )

Here is what I get:

0.185455 0.0581818 -0.0509091 -0.0509091 0.0581818
0.0581818 0.185455 0.0581818 -0.0509091 -0.0509091
-0.0509091 0.0581818 0.185455 0.0581818 -0.0509091
-0.0509091 -0.0509091 0.0581818 0.185455 0.0581818
0.0581818 -0.0509091 -0.0509091 0.0581818 0.185455

I'm pulling my hair out here! Can someone help?

Cheers,

David

--
David W. Fanning, Ph.D.
Fanning Software Consulting, Inc.
Phone: 970-221-0438, E-mail: david@dfanning.com
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Toll-Free IDL Book Orders: 1-888-461-0155

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[Message index]

		Re: Matlab Syntax By: Mark Hadfield on Thu, 20 November 2003 13:09
		Re: Matlab Syntax By: Bruce Bowler on Thu, 20 November 2003 12:58
		Re: Matlab Syntax By: Mark Hadfield on Thu, 20 November 2003 12:56
		Re: Matlab Syntax By: David Fanning on Thu, 20 November 2003 12:52
		Re: Matlab Syntax By: James Kuyper on Thu, 20 November 2003 13:44
		Re: Matlab Syntax By: David Fanning on Thu, 20 November 2003 12:38
		Re: Matlab Syntax By: Nigel Wade on Tue, 18 November 2003 02:16

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