Question

i and j are very popular variable names (see e.g., this question and this one).

For example, in loops:

for i=1:10,
    % Do something...
end

As indices into a matrix:

mat(i, j) = 4;

Why shouldn’t they be used as variable names in MATLAB?

Answer 1

Because i and j are both functions denoting the imaginary unit:

• http://www.mathworks.co.uk/help/matlab/ref/i.html
• http://www.mathworks.co.uk/help/matlab/ref/j.html

So a variable called i or j will override them, potentially silently breaking code that does complex maths.

Possible solutions include using ii and jj as loop variables instead, or using 1i whenever i is required to represent the imaginary unit.