Error: Subscript indices must either be real positive integers or logicals.

I have the following code and I am having this error

Subscript indices must either be real positive integers or logicals.

Error in ==> Markov_Chain at 64

cur_state = Rand_Vect(P(cur_state,:), 1);

How should I solve it?

Thanks

function [Chain] = Markvok_Chain( P, initial_state, n )

    P = [ 0.85 0.15; 0.05 0.95 ];
    initial_state = [0.4 0.6];
    n=20;

    sz = size(P);
    cur_state = round(initial_state);

%
% Verify that the input parameters are valid
%
if (sz(1) ~= sz(2))
   error('Markov_Chain:  Probability matrix is not square');
end
num_states = sz(1);

if (cur_state < 1) | (cur_state > num_states)
   error('Markov_Chain:  Initial state not defined in P')
end

for i=1:num_states
   if (sum(P(i,:)) ~=1 )
      error('Markov_Chain:  Transition matrix is not valid')
   end
end

%
% Create the Markov Chain 

Chain(1,1:2) = cur_state;
for i = 1:n

     cur_state = Rand_Vect(P(cur_state,:), 1);
     Chain(i,1:2) = cur_state;

end

Answer 1

[Daniel Shub]

Look at the error and then look at your code. Basically you have

cur_state = round([0.4 0.6]);

which is the same as

cur_state = [0, 1];

Now the error says "real positive integers or logicals". Since cur_state is not a logical array, all of its elements must be real positive integers, but 0 is not a positive integer.

[dpr]

Thanks, I'm getting started with matlab. Any ideas on how to make the code work?

Answer 2

[Wayne King]

cur_state is a row vector and the first element is zero. You cannot address the 0-th row or column (element) in MATLAB.

x = rand(10,1);
x(0)

produces the error you are getting.