function [patterns,labels] = gen_data_pt_b(nSamples,dim)
% GEN_DATA_PT_B - Generates simulated classification data according to the sum of 
% the squares of "dim" standard normal random variables
% 
% Written by:
% -- 
% John L. Weatherwax                2007-07-05
% 
% email: wax@alum.mit.edu
% 
% Please send comments and especially bug reports to the
% above email address.
% 
%-----

% generate "nSamples" from "dim" independent Gaussians:
% 
patterns = randn( nSamples, dim ); 

% square and sum (these are now samples from a chi^2 random variable with dim degrees of freedom): 
dt = sum( patterns.^2, 2 ); 

% calculate the threshold: for classification (if dim=10 then ct ~ 9.3)
ct = chi2inv( 0.5, dim );

indsGT = find( dt >  ct ); 
indsLT = find( dt <= ct ); 
labels(indsGT) =  1; 
labels(indsLT) = -1;