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MATLAB Mathematics - SERC - Index of

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1 Matrices and Linear Algebra<br />

Eigenvalues<br />

An eigenvalue and eigenvector <strong>of</strong> a square matrix A are a scalar λ<br />

nonzero vector v that satisfy<br />

and a<br />

Av<br />

= λv<br />

This section explains:<br />

• Eigenvalue decomposition<br />

• Problems associated with defective (not diagonalizable) matrices<br />

• The use <strong>of</strong> Schur decomposition to avoid problems associated with<br />

eigenvalue decomposition<br />

Eigenvalue Decomposition<br />

With the eigenvalues on the diagonal <strong>of</strong> a diagonal matrix Λ and the<br />

corresponding eigenvectors forming the columns <strong>of</strong> a matrix V, you have<br />

AV<br />

=<br />

VΛ<br />

If V is nonsingular, this becomes the eigenvalue decomposition<br />

A = VΛV – 1<br />

A good example is provided by the coefficient matrix <strong>of</strong> the ordinary differential<br />

equation in the previous section:<br />

A =<br />

0 -6 -1<br />

6 2 -16<br />

-5 20 -10<br />

The statement<br />

lambda = eig(A)<br />

produces a column vector containing the eigenvalues. For this matrix, the<br />

eigenvalues are complex:<br />

lambda =<br />

-3.0710<br />

-2.4645+17.6008i<br />

-2.4645-17.6008i<br />

1-38

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