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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114 Operatori liniari s¸i pozitivi<br />
8.2 B-spline<br />
∆ : t0 ≤ t1 ≤ ··· ≤ tk ≤ a ≤ ··· ≤ b ≤ tn ≤ ··· ≤ tn+k<br />
multiplicitateari +1 ≤ k +1<br />
Foarte frecvent avem<br />
t0 = t1 = ··· = tk = a < tk+1 ≤ ··· ≤ tn−1 < b = tm = ··· = tn+k<br />
<br />
1 dacăx ∈ [ti,ti+1]<br />
Bi,0(x) =<br />
0 în caz contrar<br />
⎧<br />
⎨ x−ti<br />
dacăti < ti+k<br />
ωi,k(x) = ti+k −ti<br />
⎩<br />
0 în caz contrar<br />
(8.2)<br />
Bi,k(x) = ωi,k(x)Bi,k−1(x)+(1−ωi+1,k(x))Bi+1,k−1(x) (8.3)<br />
Bi,k(x) = (ti+k+1 −ti)[ti,...,ti+k+1,(·−x) k + ]<br />
Problema 8.2.1 Să se scrie expresia funct¸iilor B-spline <strong>de</strong> grad 3 cu nodurile<br />
{ti = i|i ∈ Z}<br />
Solut¸ie. Avem<br />
Bi,k(x) = Bj+l,k(x+l),<br />
s¸i <strong>de</strong>ci este suficient să <strong>de</strong>terminăm un singur spline.<br />
Bj,k(x) = ωi,k(x)Bi,k−1(x)+(1−ωi+1,k(x))Bi+1,k−1(x) =<br />
= x−i<br />
i+k −i Bi,k−1(x)+<br />
<br />
x−i−1<br />
1−<br />
i+1+k −i−1<br />
= x−i k +i+1−x<br />
Bi,k−1(x)+ Bi+1,k−1(x)<br />
k k<br />
Bj+l,k(x+l) =<br />
Bi+1,k−1(x) =<br />
x+l −j −l<br />
i+l+k −i−l Bi+l,k−1(x+l)+<br />
<br />
<br />
x+l−i−l −1<br />
1−<br />
Bi+l+1,k−1 =<br />
i+l +1+k −i−l−1<br />
= x−i<br />
k<br />
k −i−1−x<br />
Bi+l,k−1(x+l)− Bi+l+1,k−1(x+l)<br />
k<br />
B0,3(x) = ω0,3(x)B0,2(x)+(1−ω1,3(x))B1,2(x)) = 1<br />
3 [xB0,2(x)+(4−x)B1,2(x)]<br />
B0,2(x) = ω0,2(x)B0,1(x)+(1−ω1,2(x))B1,1(x) = 1<br />
2 [xB0,1(x)+(3−x)B1,1(x)]