index exceeds matrix dimension

I am coding a problem in which the answer is a matrix and values in the matrix are filled in via loops from the last row and column backwards to the first row and column. I am getting the error "index exceeds matrix dimensions" in line 48 and I don't know why. The exact line is: VNEXT(d+1) = V(SNEXT((d+1)+1,t+1));

The entire code is:

function [ V, A ] = inventory( N ) %UNTITLED3 Summary of this function goes here % Detailed explanation goes here

% initialize PARAMETERS

FIXCOST = 1; MARGCOST = 3; HCOST = 1; PRICE = 8; MAX = 3; NSTATES = MAX - 1;

STATES = (0:MAX);

DEMAND = (0:2); PROB = [0.3; 0.3; 0.4];

V = ones(NSTATES, N) * -Inf; A = zeros(NSTATES, N);

% set terminal conditions V(:, N) = 0; A(:, N) = 1;

REV = zeros(3,1); SNEXT = zeros(3,1); VNEXT = zeros(3,1);

% Backward Induction for t = N-1:-1:1 for s = 1:MAX for a = 0:MAX - s

           if (a == 0)
               ordercost = 0;
           else
               ordercost = FIXCOST + MARGCOST * a;
           end

           u = s + a;
           holdcost = HCOST * u;

           for d = 0:2
               REV(d+1) = PRICE * min(u,d);
               SNEXT(d+1) = max(u-d,0);
               VNEXT(d+1) = V(SNEXT((d+1)+1,t+1));
           end

           ER = sum(REV .* PROB);
           EVNEXT = sum(VNEXT .* PROB);
           TOTV = ER + EVNEXT - ordercost - holdcost;

           if (V(s+1,t) < TOTV)
               V(s+1,t) = TOTV;
               A(s+1,t) = a;
           end

       end
   end
end

For the line in question I need to index the next row/column to use it in the calculation for the previous row/column value. So d+1 and t+1 must be used.

[Rik]

Use breakpoints and go through your code line by line. Apparently you are trying to access a value that is outside of you matrix. You did (try to?) account for it already (e.g. in for t = N-1:-1:1)

Also, please format your question correctly by selecting your code and then pressing the {}Code button.

Answer 1

[KL]

When d = 2,

 V(SNEXT((d+1)+1,t+1))

means

 V(SNEXT(4,t+1)) %there's no 4th row

and I don't even have to say about 't', while SNEXT is simply a column vector so, t should never be more than 0. So there you get the error.