_update_nodes_with_xyz for heterogenous nseg (#445)

* fix: update_nodes_with_xyz now works with heterogenous nseg

* fix: rm cumsum_nseg, since not present in comp / branch

jaxley/modules/base.py

@@ -123,35 +123,42 @@ def __init__(self):
     def _update_nodes_with_xyz(self):
         """Add xyz coordinates of compartment centers to nodes.
 
-        Note: For sake of performance, interpolation is not done for each branch,
-        but once along a concatenated (and padded) array of all branches.
+        Centers are the midpoint between the comparment endpoints on the morphology
+        as defined by xyzr.
+
+        Note: For sake of performance, interpolation is not done for each branch
+        individually, but only once along a concatenated (and padded) array of all branches.
+        This means for nsegs = [2,4] and normalized cum_branch_lens of [[0,1],[0,1]] we would
+        interpolate xyz at the locations comp_ends = [[0,0.5,1], [0,0.25,0.5,0.75,1]],
+        where 0 is the start of the branch and 1 is the end point at the full branch_len.
+        To avoid do this in one go we set comp_ends = [0,0.5,1,2,2.25,2.5,2.75,3], and
+        norm_cum_branch_len = [0,1,2,3] incrememting and also padding them by 1 to
+        avoid overlapping branch_lens i.e. norm_cum_branch_len = [0,1,1,2] for only
+        incrementing.
         """
-        num_branches = len(self.xyzr)
-        comp_ends = (
-            np.linspace(0, 1, self.nseg + 1).reshape(1, -1).repeat(num_branches, 0)
+        nsegs = self.nodes.groupby("branch_index")["comp_index"].nunique().to_numpy()
+
+        comp_ends = np.hstack(
+            [np.linspace(0, 1, nseg + 1) + 2 * i for i, nseg in enumerate(nsegs)]
         )
-        comp_ends = comp_ends + 2 * np.arange(num_branches).reshape(
-            -1, 1
-        )  # inter-branch padding
         comp_ends = comp_ends.reshape(-1)
-        branch_lens = []
+        cum_branch_lens = []
         for i, xyzr in enumerate(self.xyzr):
-            branch_len = np.sqrt(
-                np.sum(np.diff(xyzr[:, :3], axis=0) ** 2, axis=1)
-            ).cumsum()
-            branch_len = np.hstack([np.array([0]), branch_len])
-            max_len = branch_len.max()
-            branch_len = (
-                branch_len / (max_len if max_len > 0 else 1) + 2 * i
-            )  # add padding like above
-            branch_len[np.isnan(branch_len)] = 0
-            branch_lens.append(branch_len)
-        branch_lens = np.hstack(branch_lens)
+            branch_len = np.sqrt(np.sum(np.diff(xyzr[:, :3], axis=0) ** 2, axis=1))
+            cum_branch_len = np.cumsum(np.concatenate([np.array([0]), branch_len]))
+            max_len = cum_branch_len.max()
+            # add padding like above
+            cum_branch_len = cum_branch_len / (max_len if max_len > 0 else 1) + 2 * i
+            cum_branch_len[np.isnan(cum_branch_len)] = 0
+            cum_branch_lens.append(cum_branch_len)
+        cum_branch_lens = np.hstack(cum_branch_lens)
         xyz = np.vstack(self.xyzr)[:, :3]
-        xyz = v_interp(comp_ends, branch_lens, xyz).reshape(
-            3, num_branches, self.nseg + 1
-        )
-        centers = ((xyz[:, :, 1:] + xyz[:, :, :-1]) / 2).reshape(3, -1).T
+        xyz = v_interp(comp_ends, cum_branch_lens, xyz).T
+        centers = (xyz[:-1] + xyz[1:]) / 2  # unaware of inter vs intra comp centers
+        cum_nsegs = np.cumsum(nsegs)
+        # this means centers between comps have to be removed here
+        between_comp_inds = (cum_nsegs + np.arange(len(cum_nsegs)))[:-1]
+        centers = np.delete(centers, between_comp_inds, axis=0)
         idcs = self.nodes["comp_index"]
         self.nodes.loc[idcs, ["x", "y", "z"]] = centers
         return centers, xyz