 Usage:  {th,liks}=bigarch(theta,et)  
 
 Input:

  theta                  columns of 2x2 ARCH and GARCH parameter matrices 
                         
  et                     time series data, tx2 
                         
 Output:

  th                     elements of upper triangular 2x2 matrix of deterministic 
                         variance components and estimated columns of 2x2 ARCH 
                         and GARCH parameter matrices 
                         
  liks                   evaluated log likelihood function 
                         
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(C) MD*TECH Method and Data Technologies, 17.8.2000
