Differential Equations Solutions 177

# Differential Equations Solutions 177 - Note that as the...

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Chapter 31 Solutions: Case Study: Eigenvalues: Valuable Principles CHALLENGE 31.1. We can verify by direct computation that w m satisfies the boundary condition and that 2 w m /∂x 2 2 w m /∂y 2 is ( m 2 + 2 ) π 2 /b 2 times w m , so λ m = ( m 2 + 2 ) π 2 /b 2 . CHALLENGE 31.2. (a) The eigenvalues are λ jk = j 2 + k 2 4 π 2 for j, k = 1 , 2 , . . . . One expression for the eigenfunction is v jk = sin( ( x + 1) / 2) sin( ( y + 1) / 2) . This is not unique, since some of the eigenvalues are multiple. So, for example, λ 12 = λ 21 , and any function av 12 + bv 21 , for arbitrary scalars a and b , is an eigenfunction. Even for simple eigenvalues, the function v jj can be multiplied by an arbitrary constant, positive or negative. The first six v jk are plotted in Figure 31.1, and it is an interesting exercise to describe them in words. Note that as the eigenvalue increases, the number
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Unformatted text preview: Note that as the eigenvalue increases, the number of oscillations in the eigenfunction increases. In order to capture this behavior in a piecewise linear approximation, we need a Fner mesh for the eigenfunctions corresponding to larger eigenvalues than we do for those corresponding to smaller eigenvalues. (b) When using piecewise linear Fnite elements, the j th computed eigenvalue lies in an interval [ λ j , λ j + C j h 2 ], where h is the mesh size used in the triangulation. This is observed in our computation using the program problem1b.m , found on the website. The error plots are shown in ±igure 31.2. The horizontal axis is the 187...
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• Fall '11
• Dr.Robin
• Eigenvalues, Eigenvalue, eigenvector and eigenspace, Eigenfunction, Wm, Simple Eigenvalues, larger eigenvalues

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