Accuracy of ZHEEV and ZHEEVD

Question

I am using LAPACK to diagonalize complex Hermitian matrices. I can choose between ZHEEV and ZHEEVD. Which one of these routines is more accurate for matrices of the size 40 and a range of eigenvalues from 1E-2 to 1E1?

Answer 1

ZHEEVD uses a divide-and-conquer method to compute eigenvalues.

If your matrices are 40 x 40 and the eigenvalues are within the range [1e-2, 1e1] then you should have absolutely no numerical issues. You can use either routine.

Answer 2

I don't know the answer but,

• It probably depends on which LAPACK library you're using. There are a number of them out there, optimized for various platforms. Are you using Netlib, MKL, ACML, ??
• Why would you take a take a total stranger's word for this when you can measure it yourself?