What Makes the Secular Equation Secular in Normal Mode Analysis?

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In summary, when solving for the frequencies of normal modes in coupled oscillators, a secular equation is used. This term refers to the equation's ability to describe long period perturbations in planetary motions and its relation to the temporal, time-related world. In perturbation theory, secular terms are those found in higher-order solutions of the order unity differential equation.
  • #1
nnj
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When looking for frequencies of normal modes in coupled oscillators, one can obtain a so-called secular equation given enough information.

Why call this a secular equation? What is secular about it?
 
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  • #2
It seems that one of the first (or common) use of this kind of equation was to the description of the long period perturbations in planetary motions. So here secular refers to long time periods, ages, etc.

Similar root for the "secular" meaning non-religious. God and the sacred things were considered outside of time so the "secular" business was related to the temporary, time-related world. (the "civil", outside the church, authorities were also called "temporal").

Secular is related now to the 100 year period (in romance languages) but it used to be more general, referring to any long period or generation.
 
  • #3
In terms of normal modes, in perturbation theory, secular terms are those that are found in the higher-order solutions that solve the order unity differential equation.
 

1. What is the Secular Equation?

The Secular Equation is a mathematical formula that is used to find the eigenvalues (or characteristic roots) of a square matrix. It is commonly used in fields such as physics, engineering, and economics to solve problems involving linear systems.

2. How is the Secular Equation derived?

The Secular Equation is derived by setting the determinant of the coefficient matrix (formed by subtracting the eigenvalue from the diagonal elements of the original matrix) equal to zero. This results in a polynomial equation whose roots are the eigenvalues of the matrix.

3. What is the significance of the Secular Equation?

The Secular Equation is important because it allows us to find the eigenvalues of a square matrix, which in turn helps us to understand the behavior of linear systems and solve various mathematical problems. It also has applications in fields such as quantum mechanics and data analysis.

4. Can the Secular Equation be used for non-square matrices?

No, the Secular Equation can only be used for square matrices because it requires the matrix to have the same number of rows and columns in order to find the eigenvalues. If a matrix is not square, it is not possible to find its eigenvalues using the Secular Equation.

5. Are there any limitations to the Secular Equation?

Yes, the Secular Equation has some limitations. It can only be used for matrices with real or complex values, and it may not always yield accurate results for matrices with repeated eigenvalues or large dimensions. In such cases, numerical methods may be more appropriate for finding the eigenvalues.

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