Thanks for the comment, @mluessi, please see a longer reply below. But there do seem to be three non-zero eigenvalues for `Ck`, although one is usually at least two orders of magnitude smaller.

Here are some example `eig_vals` (each row corresponds to the eigenvalues from a different source):
[  7.95284570e+11+0.j   8.96522413e+13+0.j   1.76793301e+14+0.j]
[  1.86682869e+14+0.j   8.37232566e+13+0.j   4.22953529e+11+0.j]
[  2.80326879e+15+0.j   8.64261634e+14+0.j   9.73191616e+12+0.j]
[  1.79883392e+15+0.j   5.37690684e+14+0.j   7.44952610e+12+0.j]
[  1.18772156e+15+0.j   5.10285101e+12+0.j   3.73866310e+14+0.j]
[  7.50670759e+14+0.j   3.43915717e+12+0.j   2.89005443e+14+0.j]
[  1.80755262e+12+0.j   4.48474895e+14+0.j   2.64354606e+14+0.j]
[  1.16606323e+12+0.j   3.13012055e+14+0.j   2.25901599e+14+0.j]
[  2.98125859e+14+0.j   1.19304988e+12+0.j   1.55636908e+14+0.j]
[  2.72722758e+14+0.j   9.44017209e+11+0.j   1.18618038e+14+0.j]
[  2.45450183e+14+0.j   9.16393178e+13+0.j   5.82544576e+11+0.j]
[  3.37089764e+15+0.j   8.38183433e+14+0.j   8.32686417e+12+0.j]
[  2.56060888e+15+0.j   5.31662273e+14+0.j   5.95193934e+12+0.j]
[  1.95776926e+15+0.j   3.61711666e+12+0.j   3.87581458e+14+0.j]
[  1.31575270e+15+0.j   1.84564678e+12+0.j   3.43846398e+14+0.j]