Fix sensor output for disconnected measured components

docs/user_manual/components.md

@@ -792,6 +792,9 @@ The state estimator uses the data to evaluate the state of the grid with the hig
 
 A sensor only has output for state estimation.
 For other calculation types, sensor output is undefined.
+The sensor output attribute `energized` is derived from whether the measured object is energized at the measured
+terminal, regardless of whether the measurement is included in state estimation.
+If the measured object is not energized at the measured terminal, all residual values are zero.
 
 ### Generic Voltage Sensor
 

power_grid_model_c/power_grid_model/include/power_grid_model/main_core/output.hpp

@@ -40,6 +40,49 @@ namespace detail {
 template <typename T, typename U>
 concept assignable_to = std::assignable_from<U, T>;
 
+template <typename MeasuredComponent, class ComponentContainer, typename... StatusArgs>
+constexpr bool measured_component_active(MainModelState<ComponentContainer> const& state, Idx const obj_seq,
+                                         StatusArgs... status_args) {
+    if constexpr (common::component_container_c<ComponentContainer, MeasuredComponent>) {
+        return get_component_by_sequence<MeasuredComponent>(state.components, obj_seq).status(status_args...);
+    } else {
+        // A missing component type makes its terminal type unreachable in a valid model. Keep reduced containers
+        // compatible with the previous topology-only behavior.
+        return true;
+    }
+}
+
+template <class ComponentContainer>
+constexpr bool measured_terminal_active(MeasuredTerminalType const terminal_type,
+                                        MainModelState<ComponentContainer> const& state, Idx const obj_seq) {
+    switch (terminal_type) {
+        using enum MeasuredTerminalType;
+
+    case branch_from:
+        return measured_component_active<Branch>(state, obj_seq, BranchSide::from);
+    case branch_to:
+        return measured_component_active<Branch>(state, obj_seq, BranchSide::to);
+    case source:
+        return measured_component_active<Source>(state, obj_seq);
+    case shunt:
+        return measured_component_active<Shunt>(state, obj_seq);
+    case load:
+        [[fallthrough]];
+    case generator:
+        return measured_component_active<GenericLoadGen>(state, obj_seq);
+    case branch3_1:
+        return measured_component_active<Branch3>(state, obj_seq, Branch3Side::side_1);
+    case branch3_2:
+        return measured_component_active<Branch3>(state, obj_seq, Branch3Side::side_2);
+    case branch3_3:
+        return measured_component_active<Branch3>(state, obj_seq, Branch3Side::side_3);
+    case node:
+        return true;
+    default:
+        throw MissingCaseForEnumError{"measured_terminal_active()", terminal_type};
+    }
+}
+
 template <typename Component, typename IndexType, class ComponentContainer, non_owning_view_c ComponentOutput,
           functor_c ResFunc>
     requires model_component_state_c<MainModelState, ComponentContainer, Component> &&
@@ -247,7 +290,7 @@ constexpr auto output_result(Component const& power_sensor, MainModelState<Compo
         }
     }();
 
-    if (obj_math_id.group == disconnected) {
+    if (obj_math_id.group == disconnected || !detail::measured_terminal_active(terminal_type, state, obj_seq)) {
         return power_sensor.template get_null_output<sym>();
     }
 
@@ -317,7 +360,7 @@ constexpr auto output_result(Component const& current_sensor, MainModelState<Com
         }
     }();
 
-    if (obj_math_id.group == disconnected) {
+    if (obj_math_id.group == disconnected || !detail::measured_terminal_active(terminal_type, state, obj_seq)) {
         return current_sensor.template get_null_output<sym>();
     }