Environment Variables

With a bash shell, these are set by, e.g. (on ubuntu)

extern NEURONHOME=/where/neuron/was/installed/share/nrn


The option arguments allowed when nrniv is launched can be passed to the neuron module (import neuron) when python is launched by using the NEURON_MODULE_OPTIONS environment variable. See the output of nrniv -h for a list of these options. The relevant options are:

-NSTACK integer    size of stack (default 1000)
-NFRAME integer    depth of function call nesting (default 200)
-nogui             do not send any gui info to screen
and all InterViews and X11 options

Note that the special option -print-options will cause the neuron module to print its options (except for that one) on first import. Also, h.nrnversion(7) will return the effective command line indicating the options.

If an arg appears multiple times, only the first will take effect.


export NEURON_MODULE_OPTIONS="-nogui -NFRAME 1000 -NSTACK 10000"
python -c '
from neuron import h
  func add_recurse() {
    if ($1 == 0) { return 0 }
    return $1 + add_recurse($1 - 1)
i = 900
assert(h.add_recurse(i) == i*(i+1)/2)
assert("-nogui -NFRAME 1000 -NSTACK 10000" in h.nrnversion(7))

As the environment variable is only used on the first import of NEURON, one can set it from within python by using os.environ[NEURON_MODULE_OPTIONS] = "..." as in

import sys
assert('neuron' not in sys.modules)

import os
nrn_options = "-nogui -NSTACK 3000 -NFRAME 525"
os.environ["NEURON_MODULE_OPTIONS"] = nrn_options
from neuron import h
assert(nrn_options in h.nrnversion(7))


When set to 1, legacy unit values for FARADAY, R, and a few other constants are used. See nrn/share/lib/nrnunits.lib.in lines which begin with @LegacyY@, nrn/src/oc/hoc_init.c in the code section static struct { /* Modern, Legacy units constants */, and nrn/src/nrnoc/eion.c.

When set to 0, (default), values from codata2018 are used. See nrn/share/lib/nrnunits.lib.in lines that begin with @LegacyN@ and nrn/src/oc/nrnunits_modern.h.

Switching between legacy and modern units can also be done after launch with the top level HOC function nrnunit_use_legacy().

The purpose of allowing legacy unit values is to easily validate results of old models (double precision identity).

This environment variable takes precedence over the CMake option NRN_DYNAMIC_UNITS_USE_LEGACY.