When building Arbor you can enable backtraces in the CMake configure step by setting ARB_BACKTRACE=ON. Beware aware that this requires the Boost libraries to be installed on your system. This will cause the following additions to Arbor’s behaviour

  1. Failed assertions via asb_assert will print the corresponding stacktrace.

  2. All exceptions deriving from arbor_exception and arbor_internal_error will have stacktraces attached in the where field.

  3. Python exceptions derived from these types will add that same stacktrace information to their message.

Alternatively, you can obtain the same information using a debugger like GDB or LLDB.


Since Arbor often uses a buffer of instructions on how to construct a particular object instead of perform the action right away, errors occur not always at the location you might expect.

Consider this (adapted from

class Recipe(arb.recipe):
  # [...]
  def connections_on(self, gid):
    return [arbor.connection((src, "detector"), "syn-NOT", w, d)]

  def cell_description(self, gid):
    # [...]
    decor = (arbor.decor()
        .place('"synapse_site"', arbor.synapse("expsyn"), "syn"))
    return arbor.cable_cell(tree, labels, decor)

rec = Recipe()            # "Ok"
sim = arb.simulation(rec) # ERROR here