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Latest posts from topic “Esercizio soluzione ODES” Latest posts from topic “Esercizio soluzione ODES” on “ElectroYou”. 2016-12-09T17:51:15Z https://www.electroyou.it/forum/viewtopic.php?f=7&t=66992 Re: Esercizio soluzione ODES https://www.electroyou.it/forum/viewtopic.php?f=7&t=66992#p684136 Shika93 2016-12-12T18:46:21Z 2016-12-12T18:46:21Z
Si, è più semplice così. Trovo i coefficienti facili (C1 e C3 in questo caso) e poi C2 con Gram-Schmidt
Re: Esercizio soluzione ODES https://www.electroyou.it/forum/viewtopic.php?f=7&t=66992#p684046 DanteCpp 2016-12-12T13:56:09Z 2016-12-12T13:56:09Z
Ho controllato con matlab,

Code: Seleziona tutto
>> A = [1 0 3; 0 4 1; 2 0 2]

A =

     1     0     3
     0     4     1
     2     0     2

>> b = [1 ;0; 1]

b =

     1
     0
     1

>> t = sym('t')

t =

t

>> T=expm(A*t)

T =

[                      (3*exp(-t))/5 + (2*exp(4*t))/5,        0,                      (3*exp(4*t))/5 - (3*exp(-t))/5]
[ (2*exp(-t))/25 - (2*exp(4*t))/25 + (2*t*exp(4*t))/5, exp(4*t), (2*exp(4*t))/25 - (2*exp(-t))/25 + (3*t*exp(4*t))/5]
[                      (2*exp(4*t))/5 - (2*exp(-t))/5,        0,                      (2*exp(-t))/5 + (3*exp(4*t))/5]

>> z=T*b

z =

   exp(4*t)
t*exp(4*t)
   exp(4*t)


risulta

[unparseable or potentially dangerous latex formula]

forse hai sbagliato qualche calcolo.
Io ti consiglierei di risolvere trovando la matrice di transizione dello stato usando lo sviluppo di Sylvester o diagonalizzando la matrice.
Esercizio soluzione ODES https://www.electroyou.it/forum/viewtopic.php?f=7&t=66992#p683629 Shika93 2016-12-09T17:51:15Z 2016-12-09T17:51:15Z
Qualcuno sa dirmi se è corretto risolvere un esercizio del genere in questo modo?
Ho un problema scritto in forma matriciale:
[unparseable or potentially dangerous latex formula]

A=\begin{bmatrix}
1 & 0 & 3\\ 
0 & 4 & 1\\ 
2 & 0 & 2
\end{bmatrix}; 
\mathbf{b}=\begin{bmatrix}
1\\ 
0\\ 
1
\end{bmatrix}

La prima cosa che faccio è trovare il polinomio caratteristico di A:
[unparseable or potentially dangerous latex formula]
quindi gli autovalori, con le rispettive molteplicità sono:
[unparseable or potentially dangerous latex formula]
[unparseable or potentially dangerous latex formula]
Quindi dico che la soluzione generale sarà:
[unparseable or potentially dangerous latex formula]
A questo punto calcolo la derivata prima di z:

[unparseable or potentially dangerous latex formula]

così da poter trovare i 3 vettori. Per farlo risolvo i 3 sistemi
\begin{cases}
A\boldsymbol{C_1}=-1  \\ 
A\boldsymbol{C_2}=4\boldsymbol{C_2}+\boldsymbol{C_3} \\ 
A\boldsymbol{C_3}=4\boldsymbol{C_3} \end{cases}

E quindi i calcoli dei tre sistemi dovrebbero essere:
A\boldsymbol{C_1}=-1 \Leftrightarrow \begin{bmatrix}
1 & 0 & 3\\ 
0 & 4 & 1\\ 
2 & 0 & 2
\end{bmatrix} \begin{bmatrix}
\alpha\\ 
\beta \\ 
\gamma
\end{bmatrix}=\begin{bmatrix}
-1\\ 
-1 \\ 
-1
\end{bmatrix} \Leftrightarrow \begin{cases}
\alpha=-1/4 \\ 
\beta=-3/16 \\ 
\gamma=-1/4 
\end{cases} \Rightarrow \boldsymbol{C_1}=C_1\begin{bmatrix}
-1/4 \\ 
-3/16 \\ 
-1/4 
\end{bmatrix}

A\boldsymbol{C_2}=4\boldsymbol{C_2}+\boldsymbol{C_3} \Rightarrow \boldsymbol{C_2}=C_2\begin{bmatrix}
1\\ 
0 \\ 
1 
\end{bmatrix}+C_3 \begin{bmatrix}
1\\ 
0 \\ 
-2/3 
\end{bmatrix}

A\boldsymbol{C_3}=4\boldsymbol{C_3} \Rightarrow \boldsymbol{C_3}=C_3\begin{bmatrix}
0\\ 
1 \\ 
0 
\end{bmatrix}
dove C_1, C_2, C_3 sono una soluzione particolare.



Quindi la mia soluzione generale (se non ho cannato i calcoli) è

[unparseable or potentially dangerous latex formula]

Quindi a questo punto devo trovarmi le tre costanti C_1, C_2, C_3 calcolandomi [unparseable or potentially dangerous latex formula]
Cioè

-C_1\begin{bmatrix}
1/4 \\ 
3/16 \\ 
1/4 
\end{bmatrix}+C_2\begin{bmatrix}
1\\ 
0 \\ 
1 
\end{bmatrix}+C_3 \begin{bmatrix}
1\\ 
0 \\ 
-2/3 
\end{bmatrix}=\begin{bmatrix}
1\\ 
0 \\ 
1 
\end{bmatrix}
E se non ho sbagliato niente (ma mi interessa più che altro il procedimento)
C_1=0; C_2=1; C_3=0