Array elements that are alphabetic letters
tf = isletter('str')
tf = isletter('str') returns
an array the same size as str containing logical 1 (true)
where the elements of str are letters of the alphabet
and logical 0 (false) where
they are not.
Find the letters in character array s.
s = 'A1,B2,C3';
isletter(s)
ans =
1 0 0 1 0 0 1 0