From 2121e7cafcb26907f9e89b6929dcafd1db25e1ef Mon Sep 17 00:00:00 2001
From: Thorsten Hater <24411438+thorstenhater@users.noreply.github.com>
Date: Mon, 19 Aug 2024 17:22:04 +0200
Subject: [PATCH] We _do_ need to check.

---
 arbor/fvm_layout.cpp               | 17 ++++++++++-------
 python/test/unit/test_diffusion.py | 12 +++++++-----
 2 files changed, 17 insertions(+), 12 deletions(-)

diff --git a/arbor/fvm_layout.cpp b/arbor/fvm_layout.cpp
index 19b49cdd4..6427a9459 100644
--- a/arbor/fvm_layout.cpp
+++ b/arbor/fvm_layout.cpp
@@ -428,23 +428,26 @@ fvm_cv_discretize(const cable_cell& cell, const cable_cell_parameter_set& global
             cv_length                    += embedding.integrate_length(cable);
         }
 
-        arb_assert(cv_length > 0);
-        D.diam_um[i] = D.cv_area[i]/(cv_length*math::pi<double>);
-        D.cv_volume[i] = 0.25*D.cv_area[i]*D.diam_um[i];
+        bool has_parent = p != -1;
+        double A = D.cv_area[i];
 
-        if (D.cv_area[i]>0) {
-            auto A = D.cv_area[i];
+        if (cv_length > 0) {
+            D.diam_um[i] = A/(cv_length*math::pi<double>);
+        }
+        D.cv_volume[i] = 0.25*A*D.diam_um[i];
+
+        if (A > 0) {
             D.init_membrane_potential[i] /= A;
             D.temperature_K[i] /= A;
             // If parent is trivial, and there is no grandparent, then we can use values from this CV
             // to get initial values for the parent. (The other case, when there is a grandparent, is
             // caught below.)
-            if (p!=-1 && D.geometry.cv_parent[p]==-1 && D.cv_area[p]==0) {
+            if (has_parent && D.geometry.cv_parent[p] == -1 && D.cv_area[p] == 0) {
                 D.init_membrane_potential[p] = D.init_membrane_potential[i];
                 D.temperature_K[p] = D.temperature_K[i];
             }
         }
-        else if (p!=-1) {
+        else if (has_parent) {
             // Use parent CV to get a sensible initial value for voltage and temp on zero-size CVs.
             D.init_membrane_potential[i] = D.init_membrane_potential[p];
             D.temperature_K[i] = D.temperature_K[p];
diff --git a/python/test/unit/test_diffusion.py b/python/test/unit/test_diffusion.py
index 7fc7ee5b7..d46b879a5 100644
--- a/python/test/unit/test_diffusion.py
+++ b/python/test/unit/test_diffusion.py
@@ -6,6 +6,8 @@
 import numpy as np
 from .. import fixtures
 
+print(A.__path__)
+
 """
 Tests for the concentration and amount of diffusive particles across time and morphology.
 Three different morphological structures are considered: 1 segment ("soma only"), 2 segments
@@ -33,12 +35,12 @@ def __init__(self, cat, cell, probes, inject_remove):
         self.the_cell = cell
         self.the_probes = probes
         self.the_props = A.neuron_cable_properties()
-        self.the_props.catalogue = (
-            cat  # use the provided catalogue of diffusion mechanisms
-        )
+        # use the provided catalogue of diffusion mechanisms
+        self.the_props.catalogue = cat
+        # use diffusive particles "s"
         self.the_props.set_ion(
-            "s", valence=1, int_con=0 * U.mM, ext_con=0 * U.mM, diff=0 * U.m2 / U.s
-        )  # use diffusive particles "s"
+            "s", valence=1, int_con=0 * U.mM, ext_con=0 * U.mM, rev_pot=0 * U.mV
+        )
         self.inject_remove = inject_remove
 
     def num_cells(self):