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MATLAB Function Reference Volume 1: A - E - Bad Request

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2eig<br />

Purpose Find eigenvalues and eigenvectors<br />

Syntax d = eig(A)<br />

d = eig(A,B)<br />

[V,D] = eig(A)<br />

[V,D] = eig(A,'nobalance')<br />

[V,D] = eig(A,B)<br />

[V,D] = eig(A,B,flag)<br />

Description d = eig(A) returns a vector of the eigenvalues of matrix A.<br />

Note If S is sparse and symmetric, you can use d = eig(S) to returns the<br />

eigenvalues of S. To request eigenvectors, and in all other cases, use eigs to<br />

find the eigenvalues or eigenvectors of sparse matrices.<br />

d = eig(A,B) returns a vector containing the generalized eigenvalues, if A and<br />

B are square matrices.<br />

[V,D] = eig(A) produces matrices of eigenvalues (D) and eigenvectors (V) of<br />

matrix A, so that A*V = V*D. Matrix D is the canonical form of A—a diagonal<br />

matrix with A’s eigenvalues on the main diagonal. Matrix V is the modal<br />

matrix—its columns are the eigenvectors of A.<br />

For eig(A), the eigenvectors are scaled so that the norm of each is 1.0.<br />

If W is a matrix such that W'*A = D*W', the columns of W are the left eigenvectors<br />

of A . Use [W,D] = eig(A.'); W = conj(W) to compute the left eigenvectors.<br />

[V,D] = eig(A,'nobalance') finds eigenvalues and eigenvectors without a<br />

preliminary balancing step. Ordinarily, balancing improves the conditioning of<br />

the input matrix, enabling more accurate computation of the eigenvectors and<br />

eigenvalues. However, if a matrix contains small elements that are really due<br />

to roundoff error, balancing may scale them up to make them as significant as<br />

the other elements of the original matrix, leading to incorrect eigenvectors. Use<br />

the nobalance option in this event. See the balance function for more details.<br />

eig<br />

2-469

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