What is the meaning of the Error Mesage "Subscript indices must either be real positive integers or logicals."

What is meant By:

Subscript indices must either be real positive integers or logicals.

[Les Beckham]

The error message seems pretty clear. You cannot use an index into a matrix that is not either a real positive integer (or an array of those) or a logical (or an array of zeros and ones).

For example,

A(-1) is an error while A(1) is fine (assuming that A is defined already).

Logical indexing involves using an array of zeros and ones that specify which array elements to select (one to select, zero to ignore).

For example, if A = [0 1 2 3 4],

A(logical([0 1 0 1 0])) will be equal to [1 3].

I suggest that you read the documentation:

https://www.mathworks.com/help/matlab/math/array-indexing.html?s_tid=srchtitle

Answer 1

[KSSV]

In MATLAB the indices of an array always should be positive integers. The indices can be 0,1 if it is og logical type.

Example:

A = rand(1,10) ; 
A(1)   % no error as 1 is positve 
A(0)   % error as 0 is not allowed 
A(-1)  % error as negative indices not allowed 

Logicals:

A = rand(1,20) ; 
idx = A>0.5 ;   % idx is logical indexing with 0, 1 
class(idx)      % it says logical 
idx             % it has 0, 1
A(idx)          % logical indexing works 
id = [0 1 0 1]; 
class(id)       % double 
A(id)           % error, as indices are double 
id = logical(id) ; % convert double to logical 
A(id)           % no error