フォワードレート
r t 1 , t 2 = 1 d 2 − d 1 ( 1 + r 2 d 2 1 + r 1 d 1 − 1 ) {\displaystyle r_{t_{1},t_{2}}={\frac {1}{d_{2}-d_{1}}}\left({\frac {1+r_{2}d_{2}}{1+r_{1}d_{1}}}-1\right)}