function [ R, F ] = pp ( m )

%% PP follows a predator/prey system for M time steps.
%
  gr = 1.001; 
  dr = 0.000002; 
  df = 0.995; 
  gf = 0.0000015 ;

  R = zeros ( 1, m ); 
  F = zeros ( 1, m );

  for t = 0 : m - 1

    if ( t == 0 )
      R(t+1) = 5000;
      F(t+1) = 100;
    else
      R(t+1) = gr * R(t) - dr * F(t) * R(t);
      F(t+1) = df * F(t) + gf * F(t) * R(t);
    end

  end 

  return
end
