Culegere de probleme de Analiz˘a numeric˘a
Culegere de probleme de Analiz˘a numeric˘a
Culegere de probleme de Analiz˘a numeric˘a
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
4.2. Descompunere LUP 59<br />
cu solut¸iay = [4,2,1] T s¸i respectiv<br />
⎧<br />
⎨ x1 +2x2 +x3<br />
cu solut¸iax = [1,1,1] T .<br />
⎩<br />
x2 +x3<br />
Problema 4.2.4 Calculat¸i <strong>de</strong>scompunerea QR a matricei<br />
x2<br />
A =<br />
x3<br />
3 1<br />
4 1<br />
Solut¸ie. Reflexia pentru prima coloană este P = I − 2uuT . Vectorul u se<br />
<strong>de</strong>termină astfel:<br />
<br />
x1 +sign(x1)x<br />
ũ =<br />
2 3+5 8<br />
= = ;<br />
4 4<br />
ũ 2 = √ 8 2 +4 2<br />
u = ũ<br />
ũ 2<br />
=<br />
8<br />
4<br />
Matricea <strong>de</strong> reflexie este<br />
<br />
1 0<br />
P = −2<br />
0 1<br />
<br />
4 1 0<br />
= −2<br />
0 1<br />
Se obt¸ine<br />
<br />
3<br />
−<br />
Q = 5 −4<br />
5<br />
−4 <br />
3<br />
5 5<br />
<br />
3<br />
−<br />
R = P ·A =<br />
− 4<br />
5<br />
<br />
/4 √ 5 =<br />
√ 5<br />
2<br />
5√<br />
5<br />
5<br />
2<br />
5 5<br />
2 1<br />
5 5<br />
5 −4<br />
5<br />
3<br />
5<br />
<br />
·<br />
<br />
·<br />
=<br />
=<br />
=<br />
<br />
.<br />
√ 5<br />
2<br />
5√<br />
5<br />
5<br />
√ 5<br />
2<br />
5√<br />
5<br />
5<br />
4<br />
2<br />
1<br />
<br />
3 −<br />
=<br />
3 1<br />
4 1<br />
Problema 4.2.5 Rezolvat¸i sistemul<br />
⎡ ⎤ ⎡<br />
1 1 1<br />
⎣ 1 1 2 ⎦x = ⎣<br />
2 4 2<br />
prin <strong>de</strong>scompunere LUP.<br />
− 4<br />
5<br />
<br />
.<br />
T<br />
=<br />
5 −4<br />
5<br />
<br />
=<br />
3<br />
4<br />
8<br />
⎤<br />
⎦<br />
3<br />
5<br />
<br />
= Q T ,<br />
−5 − 7<br />
5<br />
0 − 1<br />
5<br />
<br />
.