m is the number of the last drawdown
k is the number of a drawdown, thus 1 ≤ k ≤ m
ck is the amount of drawdown k
m' is the number of the last repayment or payment of charges
I is the number of the last repayment or payment of charges
DI is the number of the last repayment or payment of charges
II. Additional assumptions for the calculation of the APRC