Matlab error : Subscript indices must either be real positive integers or logicals

Question

I have the following error in MATLAB:

??? Subscript indices must either be real positive integers or logicals.

Error in ==> Lloyd_Max at 74 D(w_count) = mean((x - centers(xq)).^2);

This is my code :

function [ xq,centers,D ] = Lloyd_Max( x,N,min_value,max_value )
%LLOYD_MAX Summary of this function goes here
%   Detailed explanation goes here

x = x';

temp = (max_value - min_value)/2^N;

count=1;
for j=0:temp:((max_value - min_value)-temp),
   centers(count) = (j + j + temp )/2;
   count = count + 1;
end

for i=1:length(centers),
   k(i) = centers(i); 
end


w_count = 0;

while((w_count < 2) || (D(w_count) - D(w_count - 1) > 1e-6))

    w_count = w_count + 1;

    count1 = 2;
    for i=2:(count-1),
       T(i) = (k(i-1) + k(i))/2;
       count1 = count1 +1 ;
    end

    T(1) = min_value;
    T(count1) = max_value; 

    index = 1;
    for j=2:count1,
        tempc = 0;
        tempk = 0;
        for k=1:10000,
            if(x(k) >= T(j-1) && x(k) < T(j))
                tempk = tempk + x(k);
                tempc = tempc + 1; 
            end
        end
        k(index) = tempk;
        k_count(index) = tempc;
        index = index + 1;
    end

    for i=1:length(k),
        k(i) = k(i)/k_count(i);
    end

    for i=1:10000,
        if (x(i) > max_value)
            xq(i) = max_value;
        elseif (x(i) < min_value)
            xq(i) = min_value;
        else
            xq(i) = x(i);
        end
    end

    for i=1:10000,
        cnt = 1;
        for l=2:count1,
           if(xq(i) > T(l-1) && xq(i) <= T(l))
               xq(i) = cnt;
           end
           cnt = cnt +1 ;
        end
    end

   D(w_count) = mean((x - centers(xq)).^2);

end



end

and i call it and have these inputs :

M = 10000
t=(randn(M,1)+sqrt(-1)*randn(M,1))./sqrt(2);
A= abs(t).^2;
[xq,centers,D] = Lloyd_Max( A,2,0,4 );

I tried to comment the while and the D, Results : I got the xq and the centers all normal, xq in the 1-4 range, centers 1-4 indexes and 0.5-3.5 range.

I dont know whats going wrong here...Please help me.

Thank in advance!

MYSTERY SOVLED!

Thank you all guys for your help! I just putted out of the while the for loop :

for i=1:10000,
        if (x(i) > max_value)
            xq(i) = max_value;
        elseif (x(i) < min_value)
            xq(i) = min_value;
        else
            xq(i) = x(i);
        end
    end

and it worked like charm.... this loop was initilizing the array again. Sorry for that. Thank you again!

Also see [this question](http://stackoverflow.com/questions/20054047/subscript-indices-must-either-be-real-positive-integers-or-logicals-generic-sol) for [the generic solution to this problem](http://stackoverflow.com/a/20054048/983722). — Dennis Jaheruddin, Nov 27 '13 at 15:44

score 1 · Answer 1 · answered Jan 15 '13 at 06:57

1

There is an assignment xq(i) = x(i) somewhere in the middle of your function, but you pass A as x from outside where you calculate A from t which is sampled by randn, so you can't promise xq is an integer.

answered Jan 15 '13 at 06:57

s.bandara

5,636
1
21
36

I don't see any `unique` in your code, and the input is randomized. Can you run the code above again and `disp(xq)` for me right before you assign `D(w_count)`? – s.bandara Jan 15 '13 at 07:05

score 0 · Answer 2 · answered Jan 15 '13 at 06:30

0

I'm not sure exactly what you are aiming to do, but your vector xq does not contain integers, it contains doubles. If you want to use a vector of indices as you do with centers(xq), all elements of the vector need to be integers.

Upon a little inspection, it looks like xq are x values, you should find some way to map them to the integer of the closest cell to which they belong (i'm guessing 'centers' represents centers of cells?)

answered Jan 15 '13 at 06:30

RussH

329
2
17

xq contains integers, when i try it manually to ans = centers(xq) works like charm. This is a non uniformity quantizer for the signal A. The xq is the produced signal after the quantize, so if i put unique(xq) the reusults are 1,2,3,4. I am geting the results from the first while loop since i commended the while loop and the D. – Siakon Jan 15 '13 at 06:44
No, as your code is written `xq` is constructed largely from the vector `x`, which is the `A` you create in your lines of input. `A` is not a vector of integers. Try editing your code to show `Nq(1:10)` the line before your error and you will see what I mean. If you get all integer values the code you are running is not the same as the code you posted. – RussH Jan 15 '13 at 07:05
I used the disp(xq) right before the D assignment( commended the D and the while loop to run it). I got the xq having values from 1 to 4 all integers. The thing is if you notoced i am reassign xq after the xq(i) = x(i) with a integer cnt. cnt can only take values from 1 to 4, but if it can take more still it will be an integer since i am incresing it by 1 only. – Siakon Jan 15 '13 at 07:09
Uncomment the `D` line and the while loop and look again. – RussH Jan 15 '13 at 07:11
Glad to hear. On Stackoverflow if your question is resolved it is helpful to click the checkmark so others can see what answered your problem. – RussH Jan 15 '13 at 07:23

Matlab error : Subscript indices must either be real positive integers or logicals

2 Answers2