 Usage:  volatility(task)  
 
 Input:

  task                   scalar: (=1) - without dividend, (=2) - with 
                         continuously paid dividend, (=3) - with a 
                         fixed dividend at the end of T, (=4) - 
                         if for exchange rate 
                         
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(C) MD*TECH Method and Data Technologies, 17.8.2000
