 Usage:  m = fastint(x,y,h1,h2,loc{,xg})  
 
 Input:

  x                      n x p matrix, the observed continuous 
                         explanatory variable, see also xg. 
                         
  y                      n x q matrix, the observed response variables 
                         
  h1                     p x 1 vector or scalar, bandwidth for the pilot 
                         estimator. It is recommended to undersmooth here. 
                         
  h2                     pg x 1 vector or scalar, bandwidth for the backfit 
                         step. Here you should smooth in an optimal way. 
                         
  loc                    {0,1,2}, degree of the local polynomial smoother used 
                         in the backfit step: 
                         0 for Nadaraya Watson, 1 local linear, 2 local quadratic 
                         
  xg                     ng x pg matrix, optional, the points on which the 
                         estimates shall be calculated. the columns of t and 
                         tg must have the same order up to column pg < = p. 
                         If grid is used, the results won t get centered! 
                         
 Output:

  m                      ng x pp matrix, where pp is pg*(loc+1). Estimates 
                         of the additive functions in column 1 to pg, the first 
                         derivatives in column (pg+1) to (2*pg) and the second 
                         derivatives in column (2*pg+1) to (3*pg). 
                         
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(C) MD*TECH Method and Data Technologies, 17.8.2000
