I'm writing a code that mostly consists of matrices manipulation and, in particular, diagonalization. I already have a code, both in python and in Fortran 90 that are able to solve my problem in a satisfactory way. I need, however, to calculate the eigenvalues and eigenvectors of my matrices in quadruple precision because the current step of my project requires extra "sensibility" in my calculations. I was looking for some kind of library (preferably in fortran, since it seems to be faster in doing these calculations) that would allow me to re-write my Fortran 90 code with the least significant alterations as possible. I have already seen that one of my options is to mess around with the source code of the standard LAPACK functions but, honestly, that seems kind of out of my reach given my computational skills, I saw also that there is a package, MPACK, that might be able to handle these calculations. The problem is that i haven't found any useful information about this other than some not so trustful hints and I don't really know how to implement it. So, long story short, I would be really grateful if someone would help me by indicating a useful Fortran 90 library that would be able to do complex matrix diagonalization in a way that I would not need to change the original code too radically, and thus saving me from having to change the source code for LAPACK libraries by myself, something that I'm not sure that i am capable of doing with my current knowledge. Thank you very much !