function x = rot13(x)
% rot13 in MATLAB

i = (x>='a' & x<='z');
x(i) = char(mod(x(i) - 'a' + 13, 26) + 'a');

i = (x>='A' & x<='Z');
x(i) = char(mod(x(i) - 'A' + 13, 26) + 'A');