Solving Linear Differential System: Eigenvalues & Exact Solutions

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Homework Help Overview

The discussion revolves around a system of first order linear differential equations represented by a tridiagonal matrix. The original poster is exploring the possibility of finding exact eigenvalues and solutions for this system, particularly given specific boundary conditions.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • The original poster attempts to clarify the structure of the matrix and its implications for solving the eigenvalue problem. Some participants question the matrix's dimensions and structure, while others suggest looking into the properties of tridiagonal matrices.

Discussion Status

The discussion is ongoing, with participants examining the matrix's structure and its implications for finding eigenvalues. There is a recognition of the need for clarity regarding the matrix's dimensions and boundary conditions, and some guidance has been offered regarding the properties of tridiagonal matrices.

Contextual Notes

There are constraints related to the matrix's dimensions, as it was noted that the matrix is not square, which raises questions about the validity of the differential equation system. The original poster acknowledges a mistake in the matrix drawing, indicating a need for accurate representation to proceed with the analysis.

aaaa202
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I am studying a system described by a set of first order linear differential equations as can be seen on the attached picture. Now I know that to solve this analytically for a given N, N denoting the matrix size, one has to find the eigenvalues of the given matrix, which translates into finding the roots of an nth order polynomial, which is in general not possible.
But if you look at the matrix on the picture, which has a special structure, would it then be possible to find the exact eigenvalues of it and then find the exact solution of the system.
I should mention that the boundary conditions are simply:
x1(0) = 1, xn(0)=0, N≥n>1
If not by an eigenvalue method are there any other ways to find an exact solution?
 

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  • matrix.png
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Physics news on Phys.org
http://en.wikipedia.org/wiki/Tridiagonal_matrix might be of some help.
In your figure, the bottom right subscripts don't conform to the pattern of those at the top left.
Did you mean
n-1,n-2 n-1,n-1, n-1,n
n,n-2 0 0
?
Or did you intend the value in the last line to be the same as the one above it:
n-1,n-2 n-1,n-1, n-1,n
n-1,n-2 0 0
?
 
No the matrix differs does not follow the pattern in the first and last row.
 
But its still tridiagonal
 
aaaa202 said:
No the matrix differs does not follow the pattern in the first and last row.

Your matrix is not square: it has n rows and (n+1) columns. Therefore, your DE system does not make sense.
 
Oh sorry the drawing is wrong. So it is a tridiagonal matrix as described in the link above but with a_NN zero and a_12 zero. Is it possible to solve the eigenvalue equation for such a matrix exactly?
 

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