 Usage:  s2 = sigma1(phi, sigma, h)  
 
 Input:

  phi                    matrix 
                         
  sigma                  vector, standard error 
                         
  h                      integer, forecast horizon 
                         
 Output:

  s2                     matrix 
                         
--------------------------------------------------------------
(C) MD*TECH Method and Data Technologies, 17.8.2000
