complete volume-to-mass transition for base attribute. closes #798 (#…

…1357)

PySDM/initialisation/init_fall_momenta.py

@@ -12,8 +12,7 @@
 
 
 def init_fall_momenta(
-    volume: np.ndarray,
-    rho_w: float,  # TODO #798 - we plan to use masses instead of volumes soon
+    water_mass: np.ndarray,
     zero: bool = False,
     terminal_velocity_approx=GunnKinzer1949,  # TODO #1155
 ):
@@ -24,24 +23,26 @@ def init_fall_momenta(
     `PySDM.attributes.physics.relative_fall_velocity.RelativeFallVelocity` attribute)
 
     Parameters:
-        - volume: a numpy array of superdroplet volumes
-        - rho_w: the density of water (generally found in formulae.constants)
+        - water_mass: a numpy array of superdroplet water masses
 
     Returns:
         - a numpy array of initial momentum values
     """
     if zero:
-        return np.zeros_like(volume)
+        return np.zeros_like(water_mass)
 
     particulator = Particulator(0, CPU(Formulae()))  # TODO #1155
 
     approximation = terminal_velocity_approx(particulator=particulator)
 
-    radii_arr = particulator.formulae.trivia.radius(volume)
+    volume_arr = particulator.formulae.particle_shape_and_density.mass_to_volume(
+        water_mass
+    )
+    radii_arr = particulator.formulae.trivia.radius(volume=volume_arr)
     radii = particulator.Storage.from_ndarray(radii_arr)
 
-    output = particulator.Storage.empty((len(volume),), dtype=float)
+    output = particulator.Storage.empty((len(water_mass),), dtype=float)
 
     approximation(output=output, radius=radii)
 
-    return output.to_ndarray() * volume * rho_w  # TODO #798 this assumes no ice
+    return output.to_ndarray() * water_mass

tests/unit_tests/initialisation/test_init_fall_momenta.py

@@ -18,54 +18,54 @@
         pytest.param(
             {
                 "multiplicity": np.array([1, 2, 3, 2]),
-                "volume": np.array(
+                "water mass": np.array(
                     [
-                        1 * si.mm**3,
-                        0.1 * si.mm**3,
-                        1 * si.mm**3,
-                        0.05 * si.mm**3,
+                        1 * si.mg,
+                        0.1 * si.mg,
+                        1 * si.mg,
+                        0.05 * si.mg,
                     ]
                 ),
-                "rho_w": 1000,  # TODO #798 - we plan to use masses instead of volumes soon
             },
-            id="",
         ),
     ),
 )
 def params_fixture(request):
     return request.param
 
 
-def test_init_to_terminal_velocity(params, backend_instance):
-    """
-    Fall momenta correctly initialized to the terminal velocity * mass.
-    """
-    env = Box(dt=1, dv=1)
-    builder = Builder(
-        n_sd=len(params["multiplicity"]), backend=backend_instance, environment=env
-    )
-    builder.request_attribute("terminal velocity")
-    particulator = builder.build(
-        attributes={"multiplicity": params["multiplicity"], "volume": params["volume"]},
-        products=(),
-    )
-
-    terminal_momentum = (
-        particulator.attributes["terminal velocity"].to_ndarray()
-        * params["volume"]
-        * params["rho_w"]
-    )
+class TestInitFallMomenta:
+    @staticmethod
+    def test_init_to_terminal_velocity(params, backend_instance):
+        """
+        Fall momenta correctly initialized to the terminal velocity * mass.
+        """
+        env = Box(dt=1, dv=1)
+        builder = Builder(
+            n_sd=len(params["multiplicity"]), backend=backend_instance, environment=env
+        )
+        builder.request_attribute("terminal velocity")
+        particulator = builder.build(
+            attributes={
+                "multiplicity": params["multiplicity"],
+                "water mass": params["water mass"],
+            },
+            products=(),
+        )
 
-    assert np.allclose(
-        init_fall_momenta(params["volume"], params["rho_w"]), terminal_momentum
-    )
+        terminal_momentum = (
+            particulator.attributes["terminal velocity"].to_ndarray()
+            * params["water mass"]
+        )
 
+        assert np.allclose(init_fall_momenta(params["water mass"]), terminal_momentum)
 
-def test_init_to_zero(params):
-    """
-    Fall momenta correctly initialized to zero.
-    """
+    @staticmethod
+    def test_init_to_zero(params):
+        """
+        Fall momenta correctly initialized to zero.
+        """
 
-    fall_momenta = init_fall_momenta(params["volume"], params["rho_w"], zero=True)
+        fall_momenta = init_fall_momenta(params["water mass"], zero=True)
 
-    assert (fall_momenta == np.zeros_like(fall_momenta)).all()
+        assert (fall_momenta == np.zeros_like(fall_momenta)).all()