ISALPHA ISALPHA Test for Alpha Characters in a String

Usage

The isalpha functions returns a logical array that is 1 
for characters in the argument string that are letters, and 
is a logical 0 for characters in the argument that are not
letters.  The syntax for its use is

   x = isalpha(s)

where s is a string.  Note that this function is not
locale sensitive, and returns a logical 1 for letters in the
classic ASCII sense (a through z, and A through Z).
