Culegere de probleme de Analiz˘a numeric˘a
Culegere de probleme de Analiz˘a numeric˘a
Culegere de probleme de Analiz˘a numeric˘a
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6.6. Interpolare spline 99<br />
s3(x) = − 1<br />
2 x+2<br />
<br />
x 3 <br />
+ −2 x− 1<br />
3 +(x−1)<br />
2<br />
3 <br />
+<br />
Pentru rest folosim teorema lui Peano<br />
ϕ(x,t) =<br />
(Rf)(x) =<br />
b<br />
<br />
1<br />
(x−t)<br />
(m−1)!<br />
m−1<br />
+ −<br />
= (x−t)+ −<br />
a<br />
ϕ(x;t)f (m) (t)dt<br />
3<br />
<br />
si(x)(xi −t)+ =<br />
i=1<br />
3<br />
si(x)(xi −t)+ =<br />
i=1<br />
<br />
1<br />
= (x−t)+ −s1(x)(−t)+ −s2(x)<br />
2 −t<br />
<br />
+<br />
−s3(1−t)+<br />
Problema 6.6.3 Fie funct¸ia f(x) = sinπx s¸i nodurile x0 = 0, x1 = 1<br />
6 , x2 =<br />
1<br />
2 , x3 = 1.<br />
Să se <strong>de</strong>termine o funct¸ie spline naturală s¸i o funct¸ie spline limitată (racordată)<br />
care aproximează pef.<br />
Solut¸ie. Vom rezolva un sistem liniar <strong>de</strong> formaAx = b.<br />
Pentru funct¸ia spline naturală avem:<br />
⎡<br />
⎢<br />
A = ⎢<br />
⎣<br />
1 0 0 ... ... 0<br />
h0 2(h0 +h1) h1 ... ... 0<br />
0 h1 2(h1 +h2) h2 ... 0<br />
... ... ... ... ... ...<br />
... ... hn−2 2(hn−1 +hn+1) hn−1<br />
0 ... ... 0 0 1<br />
⎡<br />
⎢<br />
b = ⎢<br />
⎣<br />
3<br />
hn−1<br />
0<br />
3<br />
(an −a1)− 3<br />
(a1 −a0)<br />
h1<br />
h0<br />
.<br />
(an −an−1)− 3<br />
0<br />
(an−1 −an−2)<br />
hn−2<br />
⎤<br />
⎥<br />
⎥.<br />
⎥<br />
⎦<br />
⎤<br />
⎥<br />
⎦