I am a bit confused. From thermostatics reasons, I can derive that at a small wave frequency the matrix must be symmetric. On the other side, I read for example in Chen, L. F. et al. 'Microwave Electronics - Measurement and Materials Characterization', p. 323, that the matrix is hermitian. How could such a matrix be hermitian? If it were so, in a lossy medium for example, there would be a part of energy that is simultaneously dissipated and stored in the medium. Where is the truth?