[Pkg-octave-devel] Bug#570231: Bug#570231: octave3.2: Errors in working with complex matrices on i386

[John W. Eaton]

On 17-Feb-2010, Steven De Herdt wrote:

| While working with complex matrices, I noticed strange things going on.
| Some searching showed that there is definitely something wrong:
| 
| octave3.2:2> a=orth(randn(3));
| octave3.2:3> a'*a
| ans =
| 
|    1.0000e+00  -1.0742e-16   2.2264e-16
|   -1.0742e-16   1.0000e+00  -3.1537e-17
|    2.2264e-16  -3.1537e-17   1.0000e+00
| 
| octave3.2:4> b=orth(randn(3)+J*randn(3));
| octave3.2:5> b'*b
| ans =
| 
|    1.06482 + 0.00000i   0.10484 + 0.51574i   0.14882 + 0.71172i
|    0.10484 - 0.51574i   0.90395 + 0.00000i  -0.07914 + 0.08895i
|    0.14882 - 0.71172i  -0.07914 - 0.08895i   1.06476 + 0.00000i 
| 
| The result is Hermitian, but not quite unitary.
| This also happens on octave3.0, but not on amd64 (either version).
| 
| A look through Octave's own bug reports produces e.g. 
| http://old.nabble.com/wrong-output-for-complex-scalar-product-to26766409.html and
| http://old.nabble.com/Wrong-results-for-svd-on-complex-numbers-to27079479.html ,
| so this kind of problem is not unheard of.
| 
| Depending on one's needs, this may be an 'important' bug.

I don't see this result on my system (Debian testing, amd64).

I suspect a bug in the lapack package on your system.

jwe