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\see Nishikawa, Weiss-Smith Local-Preconditioning Matrix is a Diagonal //! Matrix in the Symmetric Form of the Euler Equations, 2021. // ***************************************************************************** { auto g = g_cfg . get < tag :: mat_spec_heat_ratio > (); auto rgas = g_cfg . get < tag :: mat_spec_gas_const > (); auto p = U ( i , 0 ); auto u = U ( i , 1 ); auto v = U ( i , 2 ); auto w = U ( i , 3 ); auto T = U ( i , 4 ); auto r = p / T / rgas ; auto...