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

Question

I have one 194-by-1 matrix. When I try to find its size, I get this message:

Subscript indices must either be real positive integers or logicals.

All values are positive and logical, what is the problem?

Answer 1

Is it possible that you accidentally override the size function?

>> which size

Should give this output

built-in (C:\ X X X \toolbox\matlab\elmat\size)

If you get something like

size is a variable

Then you override the function.

To ammend this you'll have to clear the variable

>> clear size

Now you can use the function

>> size( A )

Answer 2

Can you provide your code? It should work if you do it like this:

[rows cols] = size(A);

or

rows = length(A);

Answer 3

In MATLAB, size is a function that returns the dimensions of an array (a matrix, a cell array, etc...). However, MATLAB also supports overloading. When you call size(A) (assuming A is your matrix), the MATLAB interpreter first checks if there are overloaded variables/functions with the name size.

Apparently you have a variable named size, judging by the error message, so for MATLAB size(A) means that your trying to index into the matrix size with the subscript variable A. It seems that A has one or more zero elements, and since non-positive indices in MATLAB are forbidden, this triggers the aforementioned error.

The simplest solution is to use another name for your variable size so you can call the built-in function size without any issues.