Fix error message for non-neutrally-buoyant not-single-rigid-body case (

capytaine#414)

capytaine/bodies/bodies.py

@@ -442,10 +442,10 @@ def each_hydrostatic_stiffness(self, influenced_dof_name, radiating_dof_name, *,
             else:
                 norm_hs_stiff = 0.0
         else:
-            if self.mass is not None and np.isclose(self.mass, self.disp_mass(rho), rtol=1e-4):
+            if self.mass is not None and not np.isclose(self.mass, self.disp_mass(rho=rho), rtol=1e-4):
                 raise NotImplementedError(
                         f"Trying to compute the hydrostatic stiffness for dofs {radiating_dof_name} and {influenced_dof_name}"
-                        f"of body {self.name}, which is not neutrally buoyant (mass={self.mass}, disp_mass={self.disp_mass(rho)}.\n"
+                        f"of body {self.name}, which is not neutrally buoyant (mass={self.mass}, disp_mass={self.disp_mass(rho=rho)}).\n"
                         f"This case has not been implemented in Capytaine. You need either a single rigid body or a neutrally buoyant body."
                         )
 

docs/changelog.rst

@@ -43,6 +43,8 @@ Bug fixes
 
 * Fix :meth:`~capytaine.bem.solver.BEMSolver.compute_pressure` that was broken and a relevant test. (:pull:`394`)
 
+* Fix error message when computing hydrostatic stiffness of non-neutrally-buoyant body that is not a single rigid body. (:issue:`413` and :pull:`414`)
+
 Internals
 ~~~~~~~~~
 

pytest/test_hydrostatics.py

@@ -364,6 +364,18 @@ def test_center_of_mass_joined_bodies_with_missing_mass():
     b = cpt.FloatingBody(mass=300, center_of_mass=(1, 0, 0))
     assert (a + b).center_of_mass is None
 
+def test_not_single_rigid_and_non_neutrally_buoyant_body():
+    m = cpt.mesh_sphere()
+    a = cpt.FloatingBody(
+        mesh=m, mass=100, center_of_mass=(0, 0, 0),
+        dofs=cpt.rigid_body_dofs(rotation_center=(0, 0, 0)),
+    )
+    b = cpt.FloatingBody(
+        mesh=m.translated_x(2.0), mass=300, center_of_mass=(2, 0, 0),
+        dofs=cpt.rigid_body_dofs(rotation_center=(2, 0, 0)),
+    )
+    with pytest.raises(NotImplementedError):
+        (a + b).compute_hydrostatic_stiffness()
 
 def test_non_neutrally_buoyant_stiffness():
     body = cpt.VerticalCylinder(radius=1.0, length=2.0, center=(0.0, 0.0, 0.0), nx=40, ntheta=40, nr=20)