[Insight-users] Re: On incorrect matrix inverse

Fri Nov 11 13:24:42 EST 2005

Suyash, 

You might not have enough precision in the matrix values that you are reading from the command line.  Try generating the values with more
precision from whatever tool is generating them.  Try going out to about 12 decimal places.

I have seen this before where one program computes a matrix that is supposed to be invertible, writes the matrix in ascii, another program reads that matrix and it is no longer invertible.  

Jim

-----Original Message-----
From: insight-users-bounces+millerjv=crd.ge.com at itk.org [mailto:insight-users-bounces+millerjv=crd.ge.com at itk.org]On Behalf Of Suyash P. Awate
Sent: Friday, November 11, 2005 1:06 PM
To: jiafucang; jjomier at cs.unc.edu; insight-users at itk.org
Subject: [Insight-users] Re: On incorrect matrix inverse

Hi everybody,

Thanks for the generous help.

I was also trying to get the inverse concerning with the registration application, like Fucang (see email attached).

Here is my piece of code that gave me the wrong result:

------------
const unsigned int Dimension = 3;
typedef double PixelType;
typedef itk::Matrix <PixelType, Dimension, Dimension> MatrixType;
MatrixType matrix;
  matrix.Fill (0);
  matrix (0,0)= atof (argv[4]);
  matrix (0,1)= atof (argv[5]);
  matrix (0,2)= atof (argv[6]);
  matrix (1,0)= atof (argv[7]);
  matrix (1,1)= atof (argv[8]);
  matrix (1,2)= atof (argv[9]);
  matrix (2,0)= atof (argv[10]);
  matrix (2,1)= atof (argv[11]);
  matrix (2,2)= atof (argv[12]);
vnl_matrix_fixed <PixelType, Dimension, Dimension> inverse;
inverse= matrix.GetInverse();
-----------
matrix
 0.99925   0.0371382 -0.0109982
-0.0373772 0.99905   -0.0223916
 0.0101562 0.0227859  0.999689

warnings:
InsightToolkit-2.2.0/Utilities/vxl/core/vnl/algo/vnl_svd.txx: suspicious return value (2) from SVDC
InsightToolkit-2.2.0/Utilities/vxl/core/vnl/algo/vnl_svd.txx: M is 3x3
M = [ ...
 0.9992500000000  0.0371382000000 -0.0109982000000
-0.0373772000000  0.9990500000000 -0.0223916000000
 0.0101562000000  0.0227859000000  0.9996890000000  ]

matrix inverse using vnl in itk (incorrect)
-0.982557 -0.0644525 -0.174434
-0.0677511 0.997618   0.0130162
-0.17318  -0.0246073  0.984583

matrix inverse in matlab (correct)
 0.9992   -0.0374    0.0102
 0.0371    0.9991    0.0228
-0.0110   -0.0224    0.9997
------------

I had also tried using the AffineTransform but for some reason could not get that to work and so I wrote this simple matrix code. Perhaps that was due to the same problem that Fucang reported.
Currently, however, my problem is different. As we can see I am not using any Transform class at all. Moreover I am getting warnings from the vnl_svd class, so vnl is definitely involved here.

Julien: I am giving 9 numbers (truncated: 0.99925   0.0371382 -0.0109982 -0.0373772 0.99905 -0.0223916 0.0101562 0.0227859  0.999689) to the matrix in itk and also the same numbers to the matrix in matlab. I got these numbers from the output of a separate program.
Just FYI, I have compiled ITK on Suse 10.0 using GCC 4.0. I wonder if that has anything to do with this !

Best regards,
Suyash.

----- Original Message ----- 
From:  <mailto:jiafucang at asisz.com> jiafucang 
To:  <mailto:suyash at cs.utah.edu> suyash at cs.utah.edu ;  <mailto:jjomier at cs.unc.edu> jjomier at cs.unc.edu 
Sent: Friday, November 11, 2005 7:10 AM
Subject: On incorrect matrix inverse

Hello, Suyash, Jomier,

I have reported similar problem on
 <http://public.kitware.com/pipermail/insight-users/2005-October/015441.html> http://public.kitware.com/pipermail/insight-users/2005-October/015441.html 

and added a bug 2450

 <http://www.itk.org/Bug/bug.php?op=show&bugid=2450&pos=24> http://www.itk.org/Bug/bug.php?op=show&bugid=2450&pos=24

I think it is because ITK does not computer inverse when setparameters used, and not VNL problem.

HTH

Fucang

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