function [PCcoeff, PCvec] = pca(data, N)%PCA	Principal Components Analysis%%	Description%	 PCCOEFF = PCA(DATA) computes the eigenvalues of the covariance%	matrix of the dataset DATA and returns them as PCCOEFF.  These%	coefficients give the variance of DATA along the corresponding%	principal components.%%	PCCOEFF = PCA(DATA, N) returns the largest N eigenvalues.%%	[PCCOEFF, PCVEC] = PCA(DATA) returns the principal components as well%	as the coefficients.  This is considerably more computationally%	demanding than just computing the eigenvalues.%%	See also%	EIGDEC, GTMINIT, PPCA%%	Copyright (c) Ian T Nabney (1996-2001)if nargin == 1   N = size(data, 2);endif nargout == 1   evals_only = logical(1);else   evals_only = logical(0);endif N ~= round(N) | N < 1 | N > size(data, 2)   error('Number of PCs must be integer, >0, < dim');end% Find the sorted eigenvalues of the data covariance matrixif evals_only   PCcoeff = eigdec(cov(data), N);else  [PCcoeff, PCvec] = eigdec(cov(data), N);end