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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4.3. Sisteme <strong>de</strong> ecuat¸ii 63<br />
adică<br />
=<br />
n<br />
|xj|<br />
j=1<br />
n<br />
i=1<br />
|aij| ≤<br />
n<br />
j=1<br />
|xj| max<br />
1≤j≤n<br />
Al ≤ max<br />
1≤j≤n<br />
Fie p ∈ N, 1 ≤ p ≤ n astfel încât<br />
max<br />
1≤j≤n<br />
n<br />
|aij| =<br />
i=1<br />
n<br />
i=1<br />
|aij| = x1 max<br />
1≤j≤n<br />
n<br />
|aij|.<br />
i=1<br />
n<br />
i=1<br />
s¸ix ∈ Rn astfel încât xi = δip. Avemx1 = 1.<br />
<br />
n n n <br />
<br />
Al ≥ Ax1 = |(Ax)i| = aijxj<br />
=<br />
i=1<br />
i=1<br />
j=1<br />
|aip|<br />
n<br />
i=1<br />
n<br />
|aij|,<br />
i=1<br />
|aipxp| = max<br />
1≤j≤n<br />
n<br />
i=1<br />
|aij|<br />
Problema 4.3.3 Arătat¸i că norma euclidiană, l-norma s¸i m-norma sunt norme<br />
matriciale.<br />
Problema 4.3.4 Rezolvat¸i sistemul<br />
⎧<br />
⎨<br />
⎩<br />
5x1 +x2 +x3 = 7<br />
x1 +5x2 +x3 = 7<br />
x1 +x2 +5x3 = 7<br />
utilizând metoda lui Jacobi s¸i metoda Gauss-Sei<strong>de</strong>l.<br />
De câte iterat¸ii este nevoie pentru a se putea atinge o precizie dorităε?<br />
Solut¸ie.<br />
x (k)<br />
i<br />
x (k)<br />
i<br />
= 1<br />
aii<br />
<br />
1<br />
= bi −<br />
aii<br />
⎛<br />
⎜<br />
⎝ bi −<br />
i−1<br />
j=1<br />
n<br />
j=1<br />
j=i<br />
aijx (k)<br />
j −<br />
x (0) = (0,0,0) T<br />
x (1) =<br />
aijx (k−1)<br />
j<br />
<br />
7 7 7<br />
, ,<br />
5 5 5<br />
n<br />
j=i+1<br />
⎞<br />
⎟<br />
⎠<br />
aijx (k−1)<br />
j<br />
<br />
(4.7)<br />
(4.8)