Not getting dot product of Eigen vectors in MATLAB aslo in LAPACK to zeros

I know that theoretically eigenvectors of real symmetric matrix are orthogonal to each other. So for each pair, dot product will be zero. But when I am calculating eigenvectors from real symmetric matrix using MATLAB as well as LAPACK, I am not getting dot product to zero. Can any one help me to clear about this issue? INPUT MATRIX:

 0     1     1     1     0     0     0     0
1     0     1     0     0     0     0     0
1     1     0     0     0     0     0     0
1     0     0     0     1     1     0     0
0     0     0     1     0     0     0     0
0     0     0     1     0     0     1     1
0     0     0     0     0     1     0     1
0     0     0     0     0     1     1     0


LAPACK Output: Eigenvalues: -2.00000 -1.00000 -1.00000 -1.00000 -0.41421 1.00000 2.00000 2.41421

Eigen vector matrix:(Each column is an eigen vector of Input matrix)

0.46291 0.40993 0.40433 -0.04251 -0.30389 -0.00000 -0.40825 -0.43973

-0.15430 -0.15295 -0.18080 0.72612 0.21488 0.28868 -0.40825 -0.31094

-0.15430 -0.25698 -0.22353 -0.68361 0.21488 0.28868 -0.40825 -0.31094

-0.61721 0.00000 -0.00000 0.00000 -0.30389 -0.57735 0.00000 -0.43973

0.30861 0.00000 0.00000 -0.00000 0.73366 -0.57735 0.00000 -0.18214

0.46291 -0.40993 -0.40433 0.04251 -0.30389 -0.00000 0.40825 -0.43973

-0.15430 0.70017 -0.30213 -0.04251 0.21488 0.28868 0.40825 -0.31094

-0.15430 -0.29025 0.70646 0.00000 0.21488 0.28868 0.40825 -0.31094

MATLAB output:

Eigenvalues: -2.0000 -1.0000 -1.0000 -1.0000 -0.4142 1.0000 2.0000 2.4142

Eigen vector matrix:(Each column is an eigen vector of Input matrix)

-0.4629 0.3255 -0.2001 -0.4328 0.3039 0.0000 0.4082 0.4397

0.1543 0.0179 -0.4585 0.6106 -0.2149 -0.2887 0.4082 0.3109

0.1543 -0.3434 0.6586 -0.1777 -0.2149 -0.2887 0.4082 0.3109

0.6172 -0.0000 -0.0000 -0.0000 0.3039 0.5774 0.0000 0.4397

-0.3086 0.0000 -0.0000 0.0000 -0.7337 0.5774 -0.0000 0.1821

-0.4629 -0.3255 0.2001 0.4328 0.3039 0.0000 -0.4082 0.4397

0.1543 -0.3926 -0.4577 -0.4687 -0.2149 -0.2887 -0.4082 0.3109

0.1543 0.7181 0.2576 0.0359 -0.2149 -0.2887 -0.4082 0.3109

[evacB, evalB]=eig(B)

Thank you.

• Can you post the output that you are getting? That will help us to identify what the issue is. Also include the code that you used as that will be helpful also. Feb 5, 2016 at 8:00
• Come on... It is impossible to know what is wrong if you don't show anything.
– Eff
Feb 6, 2016 at 14:58