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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62 Rezolvarea numerică a sistemelor algebrice liniare<br />
adică<br />
Ax∞ ≤ max<br />
1≤i≤n<br />
n<br />
|aij|, ∀ x ∈ R n , x∞<br />
j=1<br />
Am = max ≤ max<br />
x∞=1 1≤i≤n<br />
Fiep ∈ N, 1 ≤ p ≤ n astfel încât<br />
Alegemxastfel încât<br />
n<br />
j=1<br />
xj =<br />
|apj| = max<br />
1≤i≤n<br />
n<br />
j=1<br />
n<br />
|aij| (4.5)<br />
j=1<br />
|aij|<br />
1 dacă apj ≥ 0<br />
−1 dacă apj < 0<br />
x∞ = 1, apjxj = |apj|, ∀j = 1,n<br />
<br />
n <br />
<br />
Ax∞ = max aijxj<br />
1≤i≤n<br />
≥<br />
<br />
n <br />
<br />
apjxj<br />
=<br />
n<br />
|apj| = max<br />
(4.5),(4.6) ⇒ ” = ”.<br />
j=1<br />
j=1<br />
j=1<br />
Am = max Ax∞ ≥ max<br />
x∞=1 1≤i≤n<br />
Problema 4.3.2 Să se arate că l-norma<br />
este naturală.<br />
Solut¸ie.<br />
Al = max<br />
1≤j≤n<br />
Al := max Ax1<br />
x1=1<br />
Fiex ∈ Rn astfel încât x1 = 1<br />
n n<br />
<br />
n<br />
<br />
Ax1 = |(Ax)i| = <br />
<br />
i=1<br />
i=1<br />
j=1<br />
aijxj<br />
<br />
<br />
<br />
<br />
≤<br />
n<br />
i=1<br />
|aij|<br />
?<br />
= max<br />
1≤j≤n<br />
n<br />
i=1<br />
n<br />
|aij|,<br />
j=1<br />
n<br />
|aij| (4.6)<br />
j=1<br />
n<br />
i=1<br />
|aij|<br />
n<br />
|aij||xj| =<br />
j=1<br />
n<br />
j=1<br />
n<br />
|aij||xj| =<br />
i=1