The Carr–Madan formula writes the damped call , , as a Fourier integral in the log-strike: with ,
which on a grid in and is a discrete Fourier transform: the fast Fourier transform returns the calls on a whole grid of log-strikes at once.
Ejemplos
Example 24.4 (Three pricers, one smile)
One-year calls in chapter 10’s base Heston model, at 17 strikes from 60 to 140, against a reference (the Lewis integral by Gauss–Legendre panels to , accurate to about ; at the money it gives 6.7509). The COS method’s largest error is 0.012 with 64 terms, with 128 and with 256. Carr–Madan with interpolation between the grid’s log-strikes reaches with 1 024 points, with 4 096, and stalls near (Figure 24.1). The truncation interval matters as much as the terms. With at twelve standard deviations instead of sixteen, COS stops at however many terms it gets, because Heston’s left tail is fatter than a normal’s.