function A = A( Pe )
% =======================
% calculates the upwinding weight as a function of Peclet number
%   I am using Patankar's Power Law scheme (page 95)
%      max[ 0, (1 - 0.1 |Pe|)^5 ]
%
     A = (1 - 0.1 * abs( Pe ) ).^5;
     index = find( A < 0);
     A(index) = zeros( size(index ) );
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