Update reference documentation.

Author: djunglas

ortools/math_opt/cpp/model.h

@@ -481,6 +481,8 @@ class Model {
   // The `weights` are an implementation detail in the solver used to order the
   // `expressions`; see the Gurobi documentation for more detail:
   // https://www.gurobi.com/documentation/9.5/refman/constraints.html#subsubsection:SOSConstraints
+  // For Xpress see
+  // https://www.fico.com/fico-xpress-optimization/docs/latest/solver/optimizer/HTML/XPRSaddsets.html
   //
   // These `weights` must either be empty or the same length as `expressions`.
   // If it is empty, default weights of 1, 2, ... will be used.
@@ -540,6 +542,8 @@ class Model {
   // The `weights` are an implementation detail in the solver used to order the
   // `expressions`; see the Gurobi documentation for more detail:
   // https://www.gurobi.com/documentation/9.5/refman/constraints.html#subsubsection:SOSConstraints
+  // For Xpress see
+  // https://www.fico.com/fico-xpress-optimization/docs/latest/solver/optimizer/HTML/XPRSaddsets.html
   //
   // These `weights` must either be empty or the same length as `expressions`.
   // If it is empty, default weights of 1, 2, ... will be used.

ortools/math_opt/cpp/parameters.h

@@ -351,7 +351,8 @@ struct SolveParameters {
   // Solvers will typically not return more solutions than the solution limit,
   // but this is not enforced by MathOpt, see also b/214041169.
   //
-  // Currently supported for Gurobi and SCIP, and for CP-SAT only with value 1.
+  // Currently supported for Gurobi, Xpress and SCIP, and for CP-SAT only with
+  // value 1.
   std::optional<int32_t> solution_limit;
 
   // If unset, use the solver default. If set, it must be >= 1.

ortools/math_opt/solvers/xpress_solver.h

@@ -42,7 +42,6 @@
 namespace operations_research::math_opt {
 
 // Interface to FICO XPRESS solver
-// Largely inspired by the Gurobi interface
 class XpressSolver : public SolverInterface {
  public:
   // Creates the XPRESS solver and loads the model into it