message: Remove DIAG_KEEP option for now.
diff: @@ -483,10 +483,11 @@ void ConstrainedOperator::Mult(const Vector &x, Vector &y) const
  });
  break;
  case DIAG_KEEP:
  - // TODO: implement DIAG_KEEP for constrained operator mult
  + // Needs action of the operator diagonal on vector
  + mfem_error("ConstrainedOperator::Mult #1");
  break;
  default:
  - mfem_error("ConstrainedOperator::Mult #1");
  + mfem_error("ConstrainedOperator::Mult #2");
  break;
  }
  }
  