Description for mex function HamEig

I am trying to calculate the purely imaginary eigenvalues of a generalized Hamiltonian eigenvalue problem. To solve for the eigenvalues I found a mex file called 'HamEig' in 'C:\Program Files\MATLAB\R2020b\toolbox\shared\controllib\engine\numerics'. Through trial and error I come to the conclusion that HamEig calls the slicot subroutine MB03XD, which can not calculate the eigenvalues of generalized Hamiltonian pencils, only standard ones.

The eig function from Matlab is not suited since extracting the purely imaginary eigenvalues is only reliable if the eigensolver takes into account the symmetry of eigenvalues of Hamiltonian matrices across real and imaginary axis.

Is there documentation stating what are in- and outputs to the mex function? I can't find anything related in the Matlab documentation or on the internet.

Furthermore, is there another Hamiltonian eigensolver available for my problem, if HamEig is not suited?

If it is any helpful, i want to implement the method from the following paper: https://ieeexplore.ieee.org/document/1333225.

Thanks in advance