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[Octave-bug-tracker] [bug #49904] Inversion of a Hermitian matrix produc


From: John W. Eaton
Subject: [Octave-bug-tracker] [bug #49904] Inversion of a Hermitian matrix produces incorrect result
Date: Wed, 21 Dec 2016 19:45:46 +0000 (UTC)
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Firefox/45.0

Update of bug #49904 (project octave):

              Item Group:        Incorrect Result => Regression             

    _______________________________________________________

Follow-up Comment #2:

Here is what I see with 4.2.0:


>> Rxx = [ 1.00003 + 0.00000i  -0.68292 + 0.26406i  -0.57670 + 0.25291i  
0.34986 +  0.03335i
  -0.68292 - 0.26406i   0.94539 + 0.00000i   0.69006 - 0.03967i  -0.43847 + 
0.38619i
  -0.57670 - 0.25291i   0.69006 + 0.03967i   0.95260 + 0.00000i  -0.34734 + 
0.40728i
   0.34986 - 0.03335i  -0.43847 - 0.38619i  -0.34734 - 0.40728i   0.98356 +
0.00000i]
Rxx =

   1.00003 + 0.00000i  -0.68292 + 0.26406i  -0.57670 + 0.25291i   0.34986 +
0.03335i
  -0.68292 - 0.26406i   0.94539 + 0.00000i   0.69006 - 0.03967i  -0.43847 +
0.38619i
  -0.57670 - 0.25291i   0.69006 + 0.03967i   0.95260 + 0.00000i  -0.34734 +
0.40728i
   0.34986 - 0.03335i  -0.43847 - 0.38619i  -0.34734 - 0.40728i   0.98356 +
0.00000i

>> Rxx * inv (Rxx)
ans =

   3.8447e+03 + 4.1605e+03i  -4.2505e+02 - 5.3359e+03i   2.1636e+02 -
2.2698e+03i  -2.2737e-13 - 1.1369e-12i
   4.8212e+03 - 6.0472e+03i   4.0808e+03 + 6.5882e+03i   2.5055e+03 +
2.8447e+03i   0.0000e+00 + 1.3642e-12i
   5.6085e+03 - 5.2994e+03i   4.1757e+03 + 6.4500e+03i   2.6433e+03 +
2.2534e+03i  -6.8212e-13 + 0.0000e+00i
  -5.1015e+03 - 7.0805e+03i   1.2351e+03 - 1.1137e+04i   4.2633e-13 -
6.3810e+03i   1.0000e+00 - 2.2737e-13i

>> inv (Rxx)
ans =

   7918.16 +    0.00i   4705.22 - 5155.62i   3582.48 - 1374.29i  -2047.24 -
6383.13i
   4705.22 - 5155.62i   6155.56 +    0.00i   3022.13 + 1516.30i   2940.40 -
5126.34i
   3582.48 - 1374.29i   3022.13 + 1516.30i   1861.79 +    0.00i    181.66 -
3243.85i
  -2047.24 - 6383.13i   2940.40 - 5126.34i    181.66 - 3243.85i   5676.72 +   
0.00i


and with 4.0.3:


>> Rxx = [ 1.00003 + 0.00000i  -0.68292 + 0.26406i  -0.57670 + 0.25291i  
0.34986 +  0.03335i
  -0.68292 - 0.26406i   0.94539 + 0.00000i   0.69006 - 0.03967i  -0.43847 + 
0.38619i
  -0.57670 - 0.25291i   0.69006 + 0.03967i   0.95260 + 0.00000i  -0.34734 + 
0.40728i
   0.34986 - 0.03335i  -0.43847 - 0.38619i  -0.34734 - 0.40728i   0.98356 +
0.00000i]
Rxx =

   1.00003 + 0.00000i  -0.68292 + 0.26406i  -0.57670 + 0.25291i   0.34986 +
0.03335i
  -0.68292 - 0.26406i   0.94539 + 0.00000i   0.69006 - 0.03967i  -0.43847 +
0.38619i
  -0.57670 - 0.25291i   0.69006 + 0.03967i   0.95260 + 0.00000i  -0.34734 +
0.40728i
   0.34986 - 0.03335i  -0.43847 - 0.38619i  -0.34734 - 0.40728i   0.98356 +
0.00000i

>> Rxx * inv (Rxx)
ans =

   1.00000 + 0.00000i  -0.00000 - 0.00000i   0.00000 - 0.00000i  -0.00000 -
0.00000i
  -0.00000 - 0.00000i   1.00000 + 0.00000i  -0.00000 + 0.00000i  -0.00000 +
0.00000i
  -0.00000 - 0.00000i  -0.00000 + 0.00000i   1.00000 - 0.00000i  -0.00000 +
0.00000i
   0.00000 + 0.00000i   0.00000 + 0.00000i   0.00000 + 0.00000i   1.00000 -
0.00000i

>> inv (Rxx)
ans =

   7918.16 +    0.00i   4705.22 - 5155.62i   3582.48 - 1374.29i  -2047.24 -
6383.13i
   4705.22 + 5155.62i   6155.56 +    0.00i   3022.13 + 1516.30i   2940.40 -
5126.34i
   3582.48 + 1374.29i   3022.13 - 1516.30i   1861.79 +    0.00i    181.66 -
3243.85i
  -2047.24 + 6383.13i   2940.40 + 5126.34i    181.66 + 3243.85i   5676.72 +   
0.00i


Something seems messed up with the signs here.  I'll take a look and see if I
can spot what changed.

    _______________________________________________________

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  <http://savannah.gnu.org/bugs/?49904>

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