Let Ti, i=1, ... ,n be a set of dates, on which payments of the floating leg of an interes trate swap occur. The payoff of the floating leg of the swap at time Ti is Fi+ s where Fi is the reference rate of the floating leg and s is a constant spread. For simplicity, let’s assume that the floating and fixed payments happen on the same dates. Also, ri is the risk-free rate on the same tenor. Let N be the notional of the swap.

1. What is the fixed semiannual swap rate calculated from the risk-free rates? Please specify mathematical formula
一般利率互换中的固定利率不是提前商定的吗，这里的意思要根据risk free rate计算，应该要怎么计算啊？