Why does a commented out line generate an error

The following code throws an error

CellArray      = {  ... 
                     'X' ...
%                   ,'X' ...  
                    ,'X' ...
                };

The error is:

Dimensions of matrices being concatenated are not consistent.

If I erase the commented out line, there is no error. So my question is: why isn't commenting out a line equivalent to erasing it.

Answer 1

[Walter Roberson]

Using ... is equivalent to bringing the next line up to the end of the current line. So that code is equivalent to

CellArray      = {  'X' %                   ,'X' ...  
                    ,'X' };

The last last of those lines is not brought up to the previous one because the ... itself on the line before it has been commented out.

You need to use

CellArray      = {  ... 
                     'X' ...
  ... %                   ,'X' ...  
                    ,'X' ...
                };

Or, since ... itself acts to comment out the rest of the line,

CellArray      = {  ... 
                     'X' ...
 ...                   ,'X' ...  
                    ,'X' ...
                };

[Leo Simon]

Thanks Walter. Could you explain why ... comments out the rest of the line? I thought it was just a way of continuing two lines

[Walter Roberson]

It is by definition.

https://www.mathworks.com/help/matlab/matlab_prog/matlab-operators-and-special-characters.html

"Three or more periods at the end of a line continues the current command on the next line. If three or more periods occur before the end of a line, then MATLAB ignores the rest of the line and continues to the next line. This effectively makes a comment out of anything on the current line that follows the three periods."