modify the tranche class in exercise 4 1 to accommodate nas bonds non accelerating s 600474

Modify the Tranche class in Exercise 4.1 to accommodate NAS bonds. Non-Accelerating Senior (NAS) bonds have a fixed principal payment schedule. Usually, this schedule has no principal payments for the first few years. The bonds pay interest on their balance as do standard bonds. NAS bonds are a type of senior bond and thus their principal payment has higher priority than subordinate bonds. Among the senior bonds, principal is distributed to the NAS bonds first according to their schedules. This mechanism lowers the investor”s risk of having excessive prepayments shorten the life of the bond and decreasing its value.