 Usage:  summ=summarize(x{,xvars})  
 
 Input:

  x                      n x p matrix, the columns correspond to the variables. 
                         
  xvars                  optional, p x 1 string vector, variable names. Note, 
                         that only up to 15 characters are used. 
                         
 Output:

  summ                   string output, containing summary table. 
                         
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(C) MD*TECH Method and Data Technologies, 17.8.2000
