Main structure
###Class: Loan
-
Loan_base: _term, _current_balance, _rate, _default(bool)
- monthly_rate()
- equal_pmt_amt()
- defaulted()
- matured()
-
Loan Pool: _loan_list
- constructor(loan_list)
- add loan
- get waterfall
###Class: factors
- Class: factors
- prepayment_rate: assume fixed
- default_rate: assume fixed
- assume recovery rate = 0.4 and recovery happen immidiately
###Class: test_classes
- Class: test_loan()