 Usage:  {hopt, ch} = regbwcrit(crit, x {,h {,K} {,d} })  
 
 Input:

  crit                   string, criterion for bandwidth selection: 
                         "shi", "gcv", "aic", "fpe", "rice". 
                         
  x                      n x 2 vector, the data. 
                         
  h                      m x 1 vector, vector of bandwidths. 
                         
  K                      string, kernel function on [-1,1] or Gaussian 
                         kernel "gau". If not given, "qua" is used. 
                         
  d                      scalar, discretization binwidth. d must be smaller 
                         than h. If not given, the minimum of min(h)/3 and 
                         (max(x)-min(x))/500 is used. 
                         
 Output:

  hopt                   scalar, optimal bandwidth. 
                         
  ch                     m x 2 vector, the criterion function for h values. 
                         
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(C) MD*TECH Method and Data Technologies, 17.8.2000
