We _do_ need to check.

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];

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):