MHB Initial Value Problem for a System of Linear Differential Equations

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The discussion revolves around solving an initial value problem for a system of linear differential equations. The equations are reformulated into matrix form, and participants discuss the process of diagonalizing the matrix to decouple the equations. They explore the substitution of variables to simplify the system, leading to a set of independent equations that can be solved more easily. The final solutions are derived, but there are concerns about discrepancies when substituting back into the original equations, prompting further verification of the results. The conversation highlights the complexity of solving coupled differential equations and the importance of careful matrix manipulation.
  • #31
We have

$$A=\begin{pmatrix}-(m_0+m_1) & m_1 & 0 \\ m_1 & -(m_1+m_2+m_3) & m_3 \\ 0 & m_3 & -(m_3+m_4)\end{pmatrix}$$

$$C=\begin{pmatrix}45m_0\\20\\35m_4\end{pmatrix}$$

So, we have to solve $X=-A^{-1}C$ subject to $z>x$, right?? (Wondering)

- - - Updated - - -

I like Serena said:
I believe you're supposed to find the solution for $X = X(t)$, which contains factors $e^{\lambda t}$.
Those terms with $e^{\lambda t}$ will not and cannot be zero. (Wasntme)

We will get three relations of the form $e^{\lambda t}=0$, right?? What does this mean?? (Wondering)
 
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  • #32
mathmari said:
We have

$$A=\begin{pmatrix}-(m_0+m_1) & m_1 & 0 \\ m_1 & -(m_1+m_2+m_3) & m_3 \\ 0 & m_3 & -(m_3+m_4)\end{pmatrix}$$

$$C=\begin{pmatrix}45m_0\\20\\35m_4\end{pmatrix}$$

So, we have to solve $X=-A^{-1}C$ subject to $z>x$, right?? (Wondering)

Yep. (Smile)

- - - Updated - - -

We will get three relations of the form $e^{\lambda t}=0$, right?? What does this mean?? (Wondering)

I'm not so sure that's what we will get. How did you get it? (Wondering)
If we would, there would be no solution. (Wasntme)
 
  • #33
I like Serena said:
Yep. (Smile)

How can we find the inverse of $A$?? I got stuck right now...
 
  • #34
I like Serena said:
I'm not so sure that's what we will get. How did you get it? (Wondering)
If we would, there would be no solution. (Wasntme)

$\lambda$ is negative... So, that means that $t \rightarrow +\infty$, or not?? (Wondering)
 
  • #35
mathmari said:
$\lambda$ is negative... So, that means that $t \rightarrow +\infty$, or not?? (Wondering)

If $e^{\lambda t} = 0$. What is the reason you think it is? (Wondering)
 
  • #36
mathmari said:
How can we find the inverse of $A$?? I got stuck right now...

I'm not quite clear on the problem.
Aren't all $m_i$ values given? (Wondering)
Wouldn't it only be $m_1$ that we make variable?
 

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