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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2.4. Polinoame ortogonale 31<br />
(1) Arătat¸i că<br />
(2)<br />
(3)<br />
(4)<br />
(5)<br />
(6)<br />
(7)<br />
(8)<br />
l α n ∈ Pn s¸i 〈l α n ,lα Γ(n+α+1)<br />
m 〉 =<br />
n!<br />
(înL2 w(0,∞) cuw(x) = xαe−x ) un<strong>de</strong>Γ(s) este funct¸iaΓalui Euler <strong>de</strong>finită<br />
prin<br />
Γ(s) =<br />
∞<br />
t<br />
0<br />
s−1 e −t dt (s > 0)<br />
nl α n (x)−(2n−1+α−x)lα n−1 (x)+(n−1−α)lα n−2 (x) = 0<br />
l α+1<br />
n (x)−l α+1<br />
n−1 (x) = lα n (x)<br />
d<br />
dx lα n(x) = −l α+1<br />
n−1(x), x d<br />
dx lα n(x) = nl α n(x)−(n+α)l α n−1(x)<br />
∞<br />
n=0<br />
l α n (x) =<br />
x n<br />
n! =<br />
t n l α n (x) =<br />
n<br />
(−1) k<br />
<br />
n+α<br />
x<br />
n−k<br />
k /k!<br />
k=0<br />
n<br />
(−1) k<br />
<br />
n+α<br />
l<br />
n−k<br />
α k<br />
k=0<br />
1 xt<br />
1−t |t| < 1 (f.gen.)<br />
(1−t) α+1e−<br />
H2n(x) = (−1) n 2 2n n!l −1/1<br />
n (x 2 )<br />
H2n+1(x) = (−1) n 2 2n+1 n!xl 1/2<br />
n (x2 )<br />
Solut¸ie. (1)-(7) se <strong>de</strong>duc utilizând tehnici analoage celor din exercit¸iile prece<strong>de</strong>nte.<br />
(8) se obt¸ine <strong>de</strong>zvoltând în serieHn(x) s¸il α n(x).<br />
Problema 2.4.11 (Ecuat¸ia diferent¸ială verificată <strong>de</strong> polinoamele ortogonale) Fie<br />
w o funct¸ie pozitivă pe[a,b] astfel încât<br />
w ′ (x)<br />
w(x) =<br />
A0 +A1x<br />
B0 +B1x+B2x 2<br />
s¸i lim<br />
x→a+<br />
w(x)(B0 +B1x+B2x<br />
(sau x→b−)<br />
2 ) = 0<br />
(2.35)<br />
(B0+B1x+B2x 2 )p ′′ n +(A0+A1x+B1+B2x)p ′ n −(A1n+B2n(n+1))pn = 0 (2.36)