function [ d ] = sizeOfVariance( eigvals, t_d )
% 
% This function implements the size of variance method for selecting the
% number of significant principle components.  The method takes any
% principal components that are larger than a precentage of the total variance.
% Taken from page 38 of 
%
% Exploratory Data Analysis with MATLAB 
% by Martinez and Martinez.
%
% Written by:
% -- 
% John L. Weatherwax                2005-08-14
% 
% email: wax@alum.mit.edu
% 
% Please send comments and especially bug reports to the
% above email address.
% 
%-----

if( nargin < 2 ) 
  t_d = 0.7;
end

% make sure we have a row vector (with postive values): 
eigvals = abs(eigvals(:).'); 

% Sort eigenvalues in decreasing order:
[ eigvals ] = sort( eigvals ); eigvals = fliplr( eigvals ); 

% Compute the mean of the variances: 
mVar = mean( eigvals ); 

inds = fliplr( find( eigvals > ( mVar * t_d ) ) ); 

% Send out the first:
d = inds(1);