Update docstring on 'calculate_displacement_unit_factor.

Author: JoeZiminski

src/spikeinterface/generation/drifting_generator.py

@@ -253,14 +253,18 @@ def calculate_displacement_unit_factor(
     non_rigid_gradient: float, unit_locations: np.array, drift_start_um: np.array, drift_stop_um: np.array
 ) -> np.array:
     """
-    In the case of introducing non-rigid drift, a set of scaling
-    factors (one per unit) is generated for scaling the displacement
-    as a function of unit position.
+    Introduces a non-rigid drift across the probe, this is a linear
+    scaling of the displacement based on the unit position.
+
+    To introduce non-rigid drift, a set of scaling factors (one per unit)
+    are generated. These scale the displacement applied to each unit
+    as a function of unit position. The smaller the `non_rigid_gradient`,
+    the larger the influence of the unit position is on scaling the
+    displacement (more non-linearity).
 
     The projections of the gradient vector (x, y)
     and unit locations (x, y) are normalised to range between
     0 and 1 (i.e. based on relative location to the gradient).
-    These factors are scaled by `non_rigid_gradient`.
 
     Parameters
     ----------
@@ -270,6 +274,7 @@ def calculate_displacement_unit_factor(
         that are based on unit location. This sets the weighting given to the factors
         based on unit locations. When 1, the factors will all equal 1 (no effect),
         when 0, the scaling factor based on unit location will be used directly.
+        Smaller number results in more nonlinearity.
     unit_locations : np.array
         The unit location with shape (num_units, 2)
     drift_start_um : np.array
@@ -293,6 +298,7 @@ def calculate_displacement_unit_factor(
         factors = 1 - factors
 
     f = np.abs(non_rigid_gradient)
+    print("f", f)
     displacement_unit_factor = factors * (1 - f) + f
 
     return displacement_unit_factor