function [state, reward] = gridmove(state,action, environment)

%
%  Grid world maze  
%  
%  NISS2000    programed by K.Samejima  Aug.1, 2000
%
%
protect = environment.protect;
cliff = environment.cliff;
start = environment.start;
goal = environment.goal;

%
% state:  x,y coordinate
%
prexs = state(2); preys = state(1);

%  action 1 :East 
%  action 2 :West 
%  action 3 : South
%  action 4 : North

switch action 
case 1
   xs = prexs + 1;
   ys = preys;
case 2
   xs = prexs - 1;
   ys = preys;
case 3
   xs = prexs;
   ys = preys + 1;
case 4
   xs = prexs;
   ys = preys - 1;
end
reward = -1;
if  xs  < 1 |  xs > size(protect,2)  |  ys < 1 |  ys>size(protect,1)
   xs = prexs;
   ys = preys;
else
   if protect(ys,xs) == 1 
      xs = prexs;
      ys = preys;
   end   
   if goal == [xs,ys];
      reward = 0;
      xs = start(2);
      ys = start(1);
   end
   if cliff(ys,xs) == 1
      reward = -100;
      xs = start(2);
      ys = start(1);
   end
end

state = [ys,xs];