
Local volatility 85
2.9.2 Calibration and its meaningfulness
What do we do once we have the hedge portfolio
Π
? Can we use it in practice?
Consider a constant volatility
bσ
0
and call
P
0
the corresponding Black-Scholes
price. Let us assume that the market smile is not too strong so that
bσ
Kτ
−bσ
0
is small.
Using the above results and expanding at order one in bσ
Kτ
− bσ
0
:
P = P
0
+
Z
T
0
dτ
Z
∞
0
dK µ (τ, K)
C
Kτ
− C
0
Kτ
(2.124)
where
C
0
Kτ
is the Black-Scholes price with volatility
bσ
0
and
C
Kτ
the market price
of the vanilla option of strike K, maturity τ.
(2.124) can be interpreted as expressing the following:
26
•
Choose an implied volatility
bσ
0
for risk-managing the exotic option. ...