mixture ansatz
function Resistivity_Francke_TXd input SI.Temperature T; input SI.MassFraction X[:] "mass fraction m_NaCl/m_brine"; input SI.Density d; input SI.MolarMass MM_vec[:]; input Integer AssertLevel = 2 "when out of validity range: 0-do nothing, 1-show warnings, 2-throw error"; output SI.Resistivity rho; end Resistivity_Francke_TXd;