% perturb the 2D image function, the First Argument in input
% returns pertubed image = pimage

function pimage = perturb (p, up, g, alpha, T)
 
     % form the perturbed image
       [m,n] = size (p);
          
       % generate  random number matrix uniformly distributed 
       % over the range [-0.5,0.5]  
         rp = random ('unif',-0.5,0.5,m,n);
         %interV = 50 * sqrt(T);
	 %rp = random ('unif',-interV,interV,m,n);
       
       pimage = p + alpha .* rp;
         
     % impose non-negativity constraint
       pimage (find (pimage < 0.0) ) = 0;
       
     
     % Calculate the change in cost function
       delta_Q = cost_simannealing (pimage,up,g) - cost_simannealing (p,up,g);
       
     
     % Decide to accept the pertubation or not
       rd = random ('unif',0,1);
       
       if ( (delta_Q > 0.0)  & (exp(-delta_Q /T) < rd) )
          
	  % do not accept the perturbation 
          pimage = p;
          
       end