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Chapter 7 Eigenvalues and Eigenvectors. 7.1 Eigenvalues and eigenvectors. Eigenvalue problem: If A is an n n matrix, do there exist nonzero vectors x in Rn such that A x is a scalar multiple of x. Note:. (homogeneous system). Characteristic polynomial of A M n n :.
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Chapter 7 Eigenvalues and Eigenvectors 7.1 Eigenvalues and eigenvectors • Eigenvalue problem: If A is an nn matrix, do there exist nonzero vectors x in Rn such that Ax is a scalar multiple of x
Note: (homogeneous system) • Characteristic polynomial of AMnn: If has nonzero solutions iff . • Characteristic equation of A:
Notes: (1) If an eigenvalue 1 occurs as a multiple root (k times) for the characteristic polynomial, then1 has multiplicity k. (2) The multiplicity of an eigenvalue is greater than or equal to the dimension of its eigenspace.
7.2 Diagonalization • Diagonalization problem: For a square matrix A, does there exist an invertible matrix P such that P-1AP is diagonal? • Notes: • (1) If there exists an invertible matrix P such that , • then two square matrices A and B are called similar. • (2) The eigenvalue problem is related closely to the • diagonalization problem.
Note: Theorem 7.7 is called the Real Spectral Theorem, and the set of eigenvalues of A is called the spectrum of A.
Note: A matrix A is orthogonally diagonalizable if there exists an orthogonal matrix P such that P-1AP = D is diagonal.
If A is not diagonal: • -- Find P that diagonalizes A:
Quadratic Forms and are eigenvalues of the matrix: matrix of the quadratic form