 Usage:  hrot = denrot(x {,K {,opt}})  
 
 Input:

  x                      n x 1 vector, the data. 
                         
  K                      string, kernel function on [-1,1]^p. If not given, 
                         the Quartic kernel "qua" is used. 
                         
  opt                    string, if opt equals "robust", a robust estimate 
                         for the standard deviation of the data is used. 
                         
 Output:

  hrot                   scalar, rule-of-thumb bandwidth. 
                         
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(C) MD*TECH Method and Data Technologies, 17.8.2000
