I am using the IMSL subroutine DEVCCG for the diagonalization of general complex matrices and sometimes the program goes INTO but does not return from DEVCCG. It simply hangs up the execution of the entire program. (I have not been able to make IMSL return an error code.) I assume that the diagonalization procedure does not converge, but am not sure. 1) Could you tell me under what circumstances this could happen?
2) What kind of matrices cause such problems? For example, if there are degenerate eigenvalues, would the algorithm not work? I cannot find any information on this topic.
Your help will be greatly appreciated.