On the nature of ill-posedness of an inverse problem arising in option
On the nature of ill-posedness of an inverse problem arising in option
On the nature of ill-posedness of an inverse problem arising in option
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1336 THe<strong>in</strong><strong>an</strong>dBH<strong>of</strong>m<strong>an</strong>n<br />
7. Conclusions<br />
0.015<br />
0.01<br />
0.005<br />
estimated S–function<br />
exact S–function<br />
0<br />
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2<br />
maturity<br />
Figure 3. Po<strong>in</strong>twise reconstruction <strong>of</strong> S δ (t) (δ = 0.001, k = 50 grids on [0, 0.2]).<br />
30<br />
25<br />
20<br />
15<br />
10<br />
5<br />
error factor<br />
0<br />
0 0.1 0.2 0.3 0.4 0.5<br />
maturity<br />
0.6 0.7 0.8 0.91 Figure 4. Behaviour <strong>of</strong><br />
� �−1 ∂UBS(X,K,r,t,S(t))<br />
∂s approximat<strong>in</strong>g <strong>the</strong> error factor ϕ(t).<br />
By study<strong>in</strong>g <strong>the</strong> <strong>problem</strong> <strong>of</strong> calibrat<strong>in</strong>g a time-dependent volatility function from a termstructure<br />
<strong>of</strong> <strong>option</strong> prices <strong>an</strong>d its <strong>ill</strong>-<strong>posedness</strong> phenomena <strong>the</strong> paper tries to f<strong>ill</strong> a gap <strong>in</strong> <strong>the</strong><br />
literature <strong>of</strong> IPs <strong>in</strong> <strong>option</strong> pric<strong>in</strong>g. The explicitly available structure <strong>of</strong> <strong>the</strong> forward operator <strong>in</strong><br />
<strong>the</strong> purely time-dependent case as a composition <strong>of</strong> <strong>an</strong> <strong>in</strong>ner l<strong>in</strong>ear convolution operator <strong>an</strong>d <strong>an</strong><br />
outer nonl<strong>in</strong>ear Nemytskii operator allows us to <strong>an</strong>alyse <strong>in</strong> detail <strong>the</strong> occurr<strong>in</strong>g <strong>ill</strong>-<strong>posedness</strong><br />
phenomena <strong>an</strong>d ways <strong>of</strong> regularization. For <strong>the</strong> outer IP treated <strong>in</strong> a C-space sett<strong>in</strong>g <strong>the</strong><br />
use <strong>of</strong> arbitrage-free data acts as a specific regularizer. In <strong>an</strong>y case, however, <strong>the</strong> <strong>in</strong>ner classic