 Usage:  specd = spec(x {,width {,opt}} )  
 
 Input:

  x                      vector 
                         
  width (optional)       scalar, 0 <= width <= (rows(x)/2) 
                         
  opt (optional)         integer; If opt=1 (Default) the spectral density 
                         estimate is returned, otherwise the log spectral 
                         density estimate 
                         
 Output:

  specd                  vector 
                         
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(C) MD*TECH Method and Data Technologies, 17.8.2000
