Rebonato’s formula approximates the Black volatility of the swaption expiring at on in the market model by freezing the weights and the forwards at today’s values:
Ejemplos
Example 8.12 (Same caplets, different swaptions)
Calibrate the model to the same caplets with (forwards nearly perfectly correlated) and with (the one-year and nine-year forwards correlated at 0.04). The swaption expiring in five years into one year is priced at 25.0% of Black volatility by both (it is one forward); into five years, at 22.1% and 17.3% (Figure 8.5). On EUR 100 million, at the money (forward 2.933%, annuity 4.102), that is EUR 2.35 million against 1.84 million: 22% apart for the same caplets. Monte Carlo confirms Rebonato’s formula to within its standard errors.