message: Updated a comment.
diff: @@ -304,6 +304,7 @@ int aGMRES(const Operator &A, Vector &x, const Vector &b,
  *
  * The operators F, C, D must take input of the same size (same width).
  * Gradients of F, C, D might be needed, depending on the OptimizationSolver.
  + * When used with Hiop, gradients of C and D must be DenseMatrices.
  * F always returns a scalar value, see CalcObjective(), CalcObjectiveGrad().
  * C and D can have arbitrary heights.
  * C and D can be NULL, meaning that their constraints are not used.
  