Use of Ntuple masks and loops
                                                                             
      hi/file 2 rwn_aptuple.hbook                                                                                       
      1dhisto 20 'Distribution by grade' 12 3 15                                                                        
      max 20 700                                                                                                        
      ntuple/plot 10.grade IDH=20                                                                                       
1     NT/MASK STMASK n 3500                                                                                      
2     NT/LOOP 10 STEP=15>>STMASK(1)                                                                              
      nt/loop 10 grade>4.and.step=13>>stmask(2)                                                                         
      nt/loop 10 _                                                                                                      
      (grade=13.and.step=10).or.(grade=14.and.step=7)>>stmask(3)                                                        
      NT/PLOT 10.GRADE _                                                                                                
      STMASK(1).OR.STMASK(2).OR.STMASK(3)>>STMASK(4) OPTION=S IDH=20                                                    
3     NT/MASK STMASK P                                                                                           
4     NT/MASK STMASK C                                                                                           
      set CHHE 0.35                                                                                                     
5     EXEC LEGEND 245 9.3 10.3 610 640 'All Staff'                                                               
5     EXEC LEGEND 244 9.3 10.3 560 590 'Staff at end of grade'                                                   

1. NT/MASK perform operations with masks. A mask is a direct-access file with the name MNAME.MASK (here STMASK.MASK ). It must contain as many 32 bit words as there are events in the associated Ntuple. Masks are interesting when only a few events of a Ntuple are selected with a time consuming selection algorithm.
2. The symbol ``>>'' in NT/LOOP and NT/PLOT allows to fill the mask according to the selection function.
3. This command allows to print the definition of the mask.
4. The option `` C '' in NT/MASK close the mask.
5. A general macro to draw a legend (see next page).
6. Try NT/PLOT 10.GRADE STMASK(4) : It produce the same result as the last NT/PLOT of the macro.
7. Compare the execution time (with TIMING ) of the two following commands:

                                                                                                                      
     NTUPLE/PLOT 10.GRADE (GRADE=13.AND.STEP=10).OR.(GRADE=14.AND.STEP=7)                                                  
     NTUPLE/PLOT 10.GRADE STMASK(3)                                                                                        
   

Output of the command  NT/MASK STMASK P
                                                                   
                                                                                                                        
 =====> Current active selections in mask STMASK                                                                        
                                                                                                                        
 Bit  Nevents    Selection                                                                                              
   1      41     STEP=15                                                                                                
                                                                                                                        
   2     877     GRADE>4.AND.STEP=13                                                                                    
                                                                                                                        
   3      57     (GRADE=13.AND.STEP=10).OR.(GRADE=14.AND.STEP=7)                                                        
                                                                                                                        
   4     975     STMASK(1).OR.STMASK(2).OR.STMASK(3)                                                                    
                                                                                                                        

A general macro to draw a legend
                                                                          
      Macro Legend                                                                                                      
1     TYPE = [1]   | Type of hatches                                                                             
1     X1   = [2]   | X bottom left corner of the box.                                                            
1     X2   = [3]   | X top right corner of the box.                                                              
1     Y1   = [4]   | Y bottom left corner of the box.                                                            
1     Y2   = [5]   | Y top right corner of the box.                                                              
1     TEXT = [6]   | Text to be printed                                                                          
      Set FAIS 3                                                                                                        
      Set FASI [TYPE]                                                                                                   
      Set BORD 1                                                                                                        
      Box [X1] [X2] [Y1] [Y2]                                                                                           
      Set TXAL 03                                                                                                       
2     XT = [X2]+$GRAFINFO('?CHHE')                                                                               
2     YT = ([Y2]+[Y1])/2                                                                                         
2     Itx [XT] [YT] [TEXT]                                                                                       
      Return                                                                                                            

1. Input parameters 1 to 6 are copied into locale variables with meaningful names.
2. The text is positionned according to the text size and the box position.