Lotka-Volterramodellen - Home Page of Lars Holm Jensen
Lotka-Volterramodellen - Home Page of Lars Holm Jensen
Lotka-Volterramodellen - Home Page of Lars Holm Jensen
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24 KAPITEL 2. EKSISTENS OG ENTYDIGHED<br />
Bevis for punkt 2:<br />
Først skal følgende udtryk vurderes opadtil:<br />
∀t ∈ J : <br />
S u1(t) − S u2(t) <br />
<br />
<br />
t<br />
= <br />
<br />
f<br />
t0<br />
v, u1(v) − f v, u2(v) <br />
<br />
<br />
dv<br />
<br />
⎡<br />
<br />
<br />
t <br />
<br />
f1 v, u1(v) t0<br />
= ⎣<br />
<br />
<br />
<br />
− f1 v, u2(v) <br />
dv<br />
<br />
t <br />
f2 v, u1(v) t0<br />
<br />
− f2 v, u2(v) <br />
⎤<br />
<br />
<br />
⎦<br />
<br />
dv <br />
<br />
<br />
<br />
<br />
= <br />
t<br />
f1 v,u1(v) −f1 v,u2(v)<br />
t0 2 <br />
<br />
t<br />
dv + f2 v,u1(v) −f2 v,u2(v)<br />
t0 2 dv<br />
<br />
<br />
≤<br />
<br />
t<br />
f1 v,u1(v) −f1 v,u2(v)<br />
t0 <br />
<br />
<br />
dv<br />
+<br />
<br />
<br />
<br />
<br />
t<br />
f2 v,u1(v) −f2 v,u2(v)<br />
t0 <br />
<br />
<br />
dv<br />
<br />
≤ <br />
t <br />
dv+ <br />
t <br />
dv<br />
t<br />
f1 v,u1(v) −f1 v,u2(v)<br />
0<br />
t<br />
f2 v,u1(v) −f2 v,u2(v)<br />
(2.27)<br />
0<br />
For at kunne fortsætte vurderingen benyttes, at f opfylder en Lipschitzbetingelse:<br />
∃KT ×M > 0, ∀v ∈ T , u1, u2 ∈ M :<br />
<br />
<br />
f<br />
v, u1(v) − f v, u2(v) <br />
≤ KT ×M||u1(v) − u2(v)|| ⇒<br />
<br />
f1 v,u1(v) −f1 v,u2(v)<br />
2 <br />
+ f2 v,u1(v) −f2 v,u2(v)<br />
2 <br />
f1 v, u1(v) <br />
− f1 v, u2(v) ≤ KT ×M||u1(v) − u2(v)|| ∧<br />
<br />
f2 v, u1(v) <br />
− f2 v, u2(v) ≤ KT ×M||u1(v) − u2(v)||<br />
≤KT ×M||u1(v)−u2(v)|| ⇒<br />
Dermed kan udtryk (2.27) vurderes opadtil:<br />
<br />
t <br />
dv+ <br />
t <br />
dv<br />
t<br />
f1 v,u1(v) −f1 v,u2(v)<br />
0<br />
t<br />
f2 v,u1(v) −f2 v,u2(v)<br />
0<br />
t<br />
t<br />
≤ KT ×M||u1(v) − u2(v)||dv + KT ×M||u1(v) − u2(v)||dv<br />
t0<br />
t<br />
=2KT ×M ||u1(v) − u2(v)||dv<br />
t0<br />
t<br />
≤2KT ×M d∞(u1, u2)dv<br />
t0<br />
=2KT ×Md∞(u1, u2)(t − t0)<br />
Anvend dette samt definitionen af d∞ til at f˚a følgende:<br />
<br />
S(u1), S(u2) <br />
= sup<br />
S u1(t) − S u2(t) <br />
d∞<br />
t∈J<br />
t0<br />
≤ sup 2KT ×Md∞(u1, u2)(t − t0)<br />
t∈J<br />
= 2KT ×Md∞(u1, u2)h<br />
= αd∞(u1, u2), hvor α = 2hKT ×M