eigs with complex hermitian matrix, should I set opts.issym to 1?

If the matrix is real and symmetric, I guess it is safe to set opts.issym = 1.

But what if the matrix is complex and hermitian?

Answer 1

[Christine Tobler]

This only matters if you pass in a function handle - if you pass in a matrix, EIGS detects if it's hermitian (real or complex) directly using the ishermitian function.

And in the complex case, issym is interpreted as asking if the matrix is Hermitian.

In the new interface using Name Value arguments, the equivalent of issym would be

eigs(Afun, n, k, IsFunctionSymmetric=true)