Under some circumstances, whenever I call DEVCCG to diagonalize a general complex matrix, the program gets stuck inside and never returns. I do not even get out an error code so that I may continue with the rest of the program. I assume the iterative diagonalization inside the procedure does not converge in an allowed number of times. (I cannot access the innards of the code.) Question: Are there some matrices that will not be diagonalizable with DEVCCG? Which types of matrices it cannot handle? Thank you very much.