idx2state

Create an 8-by-13 gridworld object with "Kings" moves. For more information, see createGridWorld and Create Custom Grid World Environments.

gw = createGridWorld(8,13,"Kings");

Display the allowed actions.

gw.Actions

ans = 8×1 string
    "N"
    "S"
    "E"
    "W"
    "NE"
    "NW"
    "SE"
    "SW"

Use the action2idx function to obtain the index associated with the "SE" action.

action2idx(gw,"SE")

ans = 
7

Use the idx2action function to obtain the name of the fifth action.

idx2action(gw,5)

ans = 
"NE"

Use the state2idx function to obtain the index associated with the state "[3,5]".

state2idx(gw,"[3,5]")

ans = 
35

Use the idx2state function to obtain the name of the twenty-fifth state.

idx2state(gw,25)

ans = 
"[1,4]"

Set two terminal states.

gw.TerminalStates = ["[6,12]";"[4,8]"];

Set the rewards for reaching the terminal states, using state2idx to index the terminal states.

gw.R(:,state2idx(gw,gw.TerminalStates),:) = 10;

Set to zero the probability of transitioning out from state "[2,4]". Use state2idx to obtain the index associated with the state "[2,4]".

gw.T(state2idx(gw,"[2,4]"),:,:) = 0;

For any action, set to one the probability from transitioning from state "[2,4]" to state "[4,4]".

gw.T(state2idx(gw,"[2,4]"),state2idx(gw,"[4,4]"),:) = 1;

Use rlMDPEnv to create the grid world environment env from the GridWorld object gw.

env = rlMDPEnv(gw);

To specify a reset function that sets the state to [3,3], first, obtain the index of this state.

x0 = state2idx(env.Model,"[3,3]")

x0 = 
19

Then, create an anonymous function handle that sets the initial state to x0. The value of x0 is saved in the anonymous function workspace at definition time.

env.ResetFcn = @() x0;

Call the environment reset function, (which in turn calls the function specified in env.ResetFcn), and return the initial state.

x = reset(env)

x = 
19

Display the name of the current state.

idx2state(env.Model,x)

ans = 
"[3,3]"

Move the agent position in the southeast direction.

[xn,rn,id]=step(env,action2idx(env.Model,"SE"))

xn = 
28

rn = 
0

id = logical
   0

Use idx2state to display the name of the next state.

idx2state(env.Model,xn)

ans = 
"[4,4]"