 Usage:  ind = indexcat(y, value{, up})  
 
 Input:

  y                      n x 1 vector 
                         
  value scalar which specifies the lower band  
                         
  up                     optional, upper bound for the category 
                         
 Output:

  ind                    m x 1 vector, indices of the elements falling into 
                         the specified category, it returns -1 
                         if there are no such elements. 
                         
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(C) MD*TECH Method and Data Technologies, 17.8.2000
