I have a question on implementing inlet velocity BC in the Shan-Chen multiphase model. For calculating the interaction force, the effective mass (e.g. psi(x)) for the neighbor nodes (e.g. psi(x+e) & psi(x-e)) should be known. In the case of inlet velocity, the function psi(x-e) is out of the computational domain. How can I compute the interaction force for inlet boundary nodes? I really appreciate your kind suggestions and helps.