If, for example, I have a constraint in my model: \displaystyle \sum_{i=1}^{100} x_j = 1
and I use fix(x[23],1), automaticaly Gurobi sets x_i = 0 for all i \neq 23 or this command lead this information in the branch and bound tree?

Dear @odow, it is possible in a binary model with 100 variables, I relax only the 10 first? I know that the command relax_integrality(model) relax all variables; I want only a subset.