Hi, I have two products which are substitudes. I try to fix a system as below to mydata. Demand1 = A1 -B1*Price1 + C1*Price2 Demand2 = A2 +B2*Price1 - C2*Price2 I would expect C1 & B2 to be symmetric, If they are truly substitude. How can I enforce this symmetry when creating a system of equations via SystemFit ? -- View this message in context: http://www.nabble.com/Preserving-Symmetry-Between-Two-Equations-tp24588224p24588224.html Sent from the R help mailing list archive at Nabble.com. [[alternative HTML version deleted]]