Department of Mathematics;
Indian Institute of Technology Delhi;
New Delhi 110016;
India;
Department of Pharmacy;
University G.d’Annunzio of Chieti-Pescara;
66100 Chieti;
Italy;
Department of MEMOTEF;
University of Rome;
La Sapienza;
00161 Rome;
Italy;
Semi-Markov process; Credit ratings; Credit risky bonds; Portfolio optimization; Min-max absolute deviation;