python binding for friction coeff

Author: Huangzizhou

src/differentiable/adjoint.cpp

@@ -38,6 +38,20 @@ void define_adjoint(py::module_ &m)
       },
       py::arg("solver"));
 
+  m.def(
+      "friction_coefficient_derivative",
+      [](State &state) {
+        Eigen::VectorXd term;
+        if (state.problem->is_time_dependent())
+          AdjointTools::dJ_friction_transient_adjoint_term(state, state.get_adjoint_mat(1), state.get_adjoint_mat(0), term);
+        else
+          log_and_throw_adjoint_error(
+              "Friction coefficient derivative is only supported for transient problems!");
+
+        return term(0);
+      },
+      py::arg("solver"));
+
   m.def(
       "initial_velocity_derivative",
       [](State &state) {

src/state/state.cpp

@@ -539,6 +539,11 @@ void define_solver(py::module_ &m)
           },
           "updates obstacle displacement", py::arg("oid"), py::arg("val"),
           py::arg("interp") = std::string(""))
+      .def(
+        "set_friction_coefficient", [](State &self, const double mu) {
+          self.args["contact"]["friction_coefficient"] = mu;
+        },
+          "set friction coefficient", py::arg("mu"))
       .def(
           "set_initial_velocity",
           [](State &self, const int body_id, const Eigen::VectorXd &velocity) {