Error using for loop

i'm currently working on the discrete Wigner ville transform, wich require to use a concatenated for loops. But when i run the code i get an error message : * Subscript indices must either be real positive integers or logicals.*. a simple version of my code:

     for i = 1 :length(A)
        for k = 1:length(B)
          a = A(i+k)*A(i-k)
        end
      end

[Jos (10584)]

It would be helpful if you give

1. the actual code
2. short examples of the inputs A and B,
3. the expected output
4. the complete error message

Answer 1

[Jan]

Posting a simplified version of the real failing code has the disadvantage, that the actual problem might be concealed.

Use the debugger to examine the problem:

dbstop if error

Now your code will stop at:

a= A(i+k) * A(i-k)

when i-k is not a positive integer. Neither 0 nor negative indices are allowed in Matlab.

[Mohamed Sebnat]

exactly my code stop working at

a = A(i+k)*A(i-k)

i understand that 0 and negative indices are not allowed in Matlab, so i will reformulate my question: how can I work around this issue? in other word how can I write the same formulae with respect to Matlab Syntax?

Answer 2

[possibility]

There are two main fails in your code. Elaborating Jan's post;

(1) when i=1 and k=1, i.e. first loop, A(i-k) = A(0) fails. The first element is starting with index 1.

(2) Even if you correct (1), you will see the same error when i=length(A), k=1. Because you attempt to an index A(i+k) which is larger than length(A).

[Mohamed Sebnat]

how can I work around this tow issues, any ideas ?

Answer 3

[Muhammad Usama Sharaf SAAFI]

In first iteration , value of i and k is 1 so A(i-k) means A(0) and in matlab "0" can not be index of any array so this cause error in your case. So, i-k should not be equal to zero otherwise it will generate error.