Modify linear generic surface and stochastic classes to support stochastic linear generic surface

Author: zuorenchen

rocketpy/rocket/aero_surface/linear_generic_surface.py

@@ -13,7 +13,8 @@ def __init__(
         self,
         reference_area,
         reference_length,
-        coefficients,
+        coefficient_constants=None,
+        coefficients=None,
         center_of_pressure=(0, 0, 0),
         name="Generic Linear Surface",
     ):
@@ -41,6 +42,13 @@ def __init__(
         reference_length : int, float
             Reference length of the aerodynamic surface. Has the unit of meters.
             Commonly defined as the rocket's diameter.
+        coefficient_constants: list, optional
+            List of constants to be populated to the coefficients. This
+            list will overwrite the coefficients dict if not None. The order is
+            as follows: [cL_0, cL_alpha, cL_beta, cL_p, cL_q, cL_r, cQ_0, cQ_alpha,
+            cQ_beta, cQ_p, cQ_q, cQ_r, cD_0, cD_alpha, cD_beta, cD_p, cD_q, cD_r,
+            cm_0, cm_alpha, cm_beta, cm_p, cm_q, cm_r, cn_0, cn_alpha, cn_beta,
+            cn_p, cn_q, cn_r, cl_0, cl_alpha, cl_beta, cl_p, cl_q, cl_r].
         coefficients: dict, optional
             List of coefficients. If a coefficient is omitted, it is set to 0.
             The valid coefficients are:\n
@@ -157,6 +165,36 @@ def __init__(
         name : str
             Name of the aerodynamic surface. Default is 'GenericSurface'.
         """
+        self.coefficient_constants = coefficient_constants
+        # Populate the coefficients from the list of constants if they are not defined
+        if coefficients is None:
+            coefficients = self._get_default_coefficients()
+        if coefficient_constants is not None:
+            # helper to build a 7‑input callable returning a fixed value
+            def _constant_factory(value):
+                def _constant(
+                    alpha, beta, mach, reynolds, pitch_rate, yaw_rate, roll_rate
+                ):
+                    """Return the captured constant regardless of inputs."""
+                    return value
+
+                return _constant
+
+            for i, key in enumerate(self._get_default_coefficients().keys()):
+                const = coefficient_constants[i]
+                coefficients[key] = Function(
+                    _constant_factory(const),
+                    inputs=[
+                        "alpha",
+                        "beta",
+                        "mach",
+                        "reynolds",
+                        "pitch_rate",
+                        "yaw_rate",
+                        "roll_rate",
+                    ],
+                    outputs=[key],
+                )
 
         super().__init__(
             reference_area=reference_area,

rocketpy/stochastic/stochastic_aero_surfaces.py

@@ -6,6 +6,7 @@
 from rocketpy.rocket.aero_surface import (
     AirBrakes,
     EllipticalFins,
+    LinearGenericSurface,
     NoseCone,
     RailButtons,
     Tail,
@@ -546,3 +547,91 @@ def create_object(self):
         )
         air_brakes.drag_coefficient *= generated_dict["drag_coefficient_curve_factor"]
         return air_brakes
+
+
+class StochasticLinearGenericSurface(StochasticModel):
+    """A Stochastic Linear Generic Surface class that inherits from StochasticModel.
+
+    See Also
+    --------
+    :ref:`stochastic_model` and
+    :class:`LinearGenericSurface <rocketpy.LinearGenericSurface>`
+
+    Attributes
+    ----------
+    object : LinearGenericSurface
+        LinearGenericSurface object to be used for validation.
+    reference_area : tuple, list, int, float
+        Reference area of the aerodynamic surface. Has the unit of meters
+        squared. Commonly defined as the rocket's cross-sectional area.
+    reference_length : tuple, list, int, float
+        Reference length of the aerodynamic surface. Has the unit of meters.
+        Commonly defined as the rocket's diameter.
+    center_of_pressure : tuple, optional
+        Application point of the aerodynamic forces and moments. The
+        center of pressure is defined in the local coordinate system of the
+        aerodynamic surface.
+    coefficient_curve_factor : tuple, list, int, float, optional
+        The drag curve factor of the air brakes. This value scales the
+        drag coefficient curve to introduce stochastic variability.
+    name : list[str]
+        List with the name of the object. This attribute can not be randomized.
+    """
+
+    def __init__(
+        self,
+        linear_generic_surface,
+        reference_area=None,
+        reference_length=None,
+        coefficient_constants=None,
+        center_of_pressure=None,
+    ):
+        """Initializes the Stochastic Linear Generic Surface class.
+
+        See Also
+        --------
+        :ref:`stochastic_model`
+
+        Parameters
+        ----------
+        linear_generic_surface : LinearGenericSurface
+            LinearGenericSurface object to be used for validation.
+        reference_area : int, float
+            Reference area of the aerodynamic surface. Has the unit of meters
+            squared. Commonly defined as the rocket's cross-sectional area.
+        reference_length : int, float
+            Reference length of the aerodynamic surface. Has the unit of meters.
+            Commonly defined as the rocket's diameter.
+        coefficients : dict
+            Dictionary containing the aerodynamic coefficients of the surface.
+        center_of_pressure : tuple, optional
+            Application point of the aerodynamic forces and moments. The center of pressure is defined in the local coordinate system of the
+        coefficient_curve_factor : tuple, list, int, float, optional
+            The drag curve factor of the air brakes. This value scales the
+            drag coefficient curve to introduce stochastic variability.
+        """
+        super().__init__(
+            linear_generic_surface,
+            reference_area=reference_area,
+            reference_length=reference_length,
+            coefficient_constants=coefficient_constants,
+            center_of_pressure=center_of_pressure,
+            name=None,
+        )
+
+    def create_object(self):
+        """Creates and returns a LinearGenericSurface object from the randomly generated input arguments.
+
+        Returns
+        -------
+        linear_generic_surface : LinearGenericSurface
+            LinearGenericSurface object with the randomly generated input arguments.
+        """
+        generated_dict = next(self.dict_generator())
+        linear_generic_surface = LinearGenericSurface(
+            reference_area=generated_dict["reference_area"],
+            reference_length=generated_dict["reference_length"],
+            coefficient_constants=generated_dict["coefficient_constants"],
+            center_of_pressure=generated_dict["center_of_pressure"],
+        )
+        return linear_generic_surface

rocketpy/stochastic/stochastic_rocket.py

@@ -11,6 +11,7 @@
 from rocketpy.rocket.aero_surface import (
     AirBrakes,
     EllipticalFins,
+    LinearGenericSurface,
     NoseCone,
     RailButtons,
     Tail,
@@ -25,6 +26,7 @@
 from .stochastic_aero_surfaces import (
     StochasticAirBrakes,
     StochasticEllipticalFins,
+    StochasticLinearGenericSurface,
     StochasticNoseCone,
     StochasticRailButtons,
     StochasticTail,
@@ -419,6 +421,36 @@ def add_air_brakes(self, air_brakes, controller):
         self.air_brakes.append(air_brakes)
         self.air_brake_controller = controller
 
+    def add_linear_generic_surface(self, linear_generic_surface, position=None):
+        """Adds a stochastic linear generic surface to the stochastic rocket.
+
+        Parameters
+        ----------
+        linear_generic_surface : StochasticLinearGenericSurface or LinearGenericSurface
+            The linear generic surface to be added to the stochastic rocket.
+        position : tuple, list, int, float, optional
+            The position of the linear generic surface.
+        """
+        if not isinstance(
+            linear_generic_surface,
+            (StochasticLinearGenericSurface, LinearGenericSurface),
+        ):
+            raise TypeError(
+                "`linear_generic_surface` must be of LinearGenericSurface or "
+                "StochasticLinearGenericSurface type"
+            )
+        if isinstance(linear_generic_surface, LinearGenericSurface):
+            linear_generic_surface = StochasticLinearGenericSurface(
+                linear_generic_surface=linear_generic_surface
+            )
+        self._add_surfaces(
+            linear_generic_surface,
+            position,
+            LinearGenericSurface,
+            StochasticLinearGenericSurface,
+            "`linear_generic_surface` must be of LinearGenericSurface or StochasticLinearGenericSurface type",
+        )
+
     def add_cp_eccentricity(self, x=None, y=None):
         """Moves line of action of aerodynamic forces to simulate an
         eccentricity in the position of the center of pressure relative