atefeh Behzadi

Thank you.  Here is file link of my code. https://www.filemail.com/d/xldiqdqckummbbe  for example if i set the objective function without the D_edge variable it works well( such as this file), but ...

this constraint is related to the determination of pipe sizes in district heating network. D_edge is diameter of each pipe, mass_edge is mass rate in each pipe and Bp is binary variable for selecti...

Thanks for your response.  This is constraint in my code: for edge in df_edges.index:       model.addConstr((D_edge[edge] * D_edge[edge]) >= (4 * 10e6 * mass_edge[edge] * Bp[edge]) /        (3600 *...