 Usage:  z = string (str, from, to)  
 
 Input:

  str                    n x 1 string vector 
                         
  from                   n x 1 vector 
                         
  to                     n x 1 vector 
                         
 Output:

  z                      n x 1 string vector 
                         
--------------------------------------------------------------
(C) MD*TECH Method and Data Technologies, 17.8.2000
