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\param[in] pos Position at which the three vector components are in U // ***************************************************************************** { Assert ( U . nunk () == D . size (), "Size mismatch" ); // Lambda to compute the velocity divergence contribution for edge p-q auto div = [ & ]( const tk :: real d [], std :: size_t p , std :: size_t q ){ return d [ 0 ] * ( U ( p , pos + 0 ) + U ( q , pos + 0 )) + d [ 1 ] * ( U ( p , pos + 1 ) + U ( q , pos + 1 )) + d [ 2 ] * ( U ( p , pos + 2 ) + U ( q ,...