function [ w_i, data ] = prob_4_7(Niter)
% PROB_4_7 - 
% 
% Written by:
% -- 
% John L. Weatherwax                2005-08-04
% 
% email: wax@alum.mit.edu
% 
% Please send comments and especially bug reports to the
% above email address.
% 
%-----

data = [ 1 1 -1 0 2;
         0 0 1 2 0;
         -1 -1 1 1 0;
         4 0 1 2 1;
         -1 1 1 1 0;
         -1 -1 -1 1 0;
        -1 1 1 2 1 ];
class = [ 2 1 2 1 1 1 2 ];

d = 0.1;
w_i = [ 1 1 1 -1 -1 1 ];

%
% Code begins:
%---

% Append +1 to all data: 
data = [ data, ones(size(data,1),1) ]; 
% Negate the feature vector from class 2:
ind = find( class==2 ); 
data(ind,:) = -data(ind,:); clear ind;

w_history = zeros( Niter, length(w_i) ); 
for ni=0:Niter+1,
  si  = mod( ni, size(data,1) )+1;
  y_i = data( si, : ).';
  v_i = y_i;
  e_i = 1; 
  
  if( w_i * y_i < d )             % This element is INCORRECTLY classified
    f2Prime = 2 * ( d - w_i * y_i ); 
    w_ip1 = w_i + e_i * f2Prime * y_i.';
  else
    w_ip1 = w_i;                  % This element is   CORRECTLY classified
  end

  % Save w iterates:
  w_history( ni+1, : ) = w_i; 
  
  % Prepare for next iteration:
  w_i = w_ip1; 
end

w_history(end-4:end,:)

% $$$ % Plot results:
% $$$ w_plot = w_history( 1:10:end, : ); 
% $$$ figure; plot( w_plot, '-o' );