topic Re: sgeev giving incorrect results in Intel® oneAPI Math Kernel Library

sgeev giving incorrect results

fantaman — Sun, 23 Nov 2025 22:12:34 GMT

Hi.

Just compiling the LAPACK examples of 2025.3 on Visual Studio. I'm getting wrong output eigenvectors for sgeev by column. The same example run with dgeev (by column) is correct. The only difference should be float vs double, but output changes. I checked the calcs and sgeev is wrong. The first (and therefore second too) left eigenvector has the opposite sign, the first and third right eigenvectors (and therefore second and fourth too) the same. The rest is correct.

It cannot be the way parameters are passed, dgeev would be wrong too.

Output attached.

Thank you

Re: sgeev giving incorrect results

Fengrui — Mon, 24 Nov 2025 21:27:13 GMT

Flipping the sign of a (right) eigenvector still gives a (right) eigenvector with the same eigenvalue, A(-v)=-Av=-\lambda v=\lambda (-v). That's also true for left eigenvectors.

Re: sgeev giving incorrect results

fantaman — Tue, 25 Nov 2025 19:36:32 GMT

I need to refresh my maths!