 Usage:  y = genarch(a, b, n)  
 
 Input:

  a                      (q+1)-vector of constant and ARCH parameters 
                         
  b                      p-vector of GARCH parameters 
                         
  n                      scalar, length of output process 
                         
 Output:

  y                      n-vector, the GARCH process 
                         
  s2                     n-vector, the volatility process 
                         
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(C) MD*TECH Method and Data Technologies, 17.8.2000
