Simulator optimized for large scale neural network simulations.
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Optimised simulator engine for NEURON

CoreNEURON is a simplified engine for the NEURON simulator optimised for both memory usage and computational speed. Its goal is to simulate massive cell networks with minimal memory footprint and optimal performance.

If you are a new user and would like to use CoreNEURON, this tutorial will be a good starting point to understand complete workflow of using CoreNEURON with NEURON.


CoreNEURON supports limited features provided by NEURON. Contact Michael Hines for detailed information.


Mod2c build

MOD2C is actually downloaded and built automatically if you have used --recursive option to clone this repository. otherwise you need to execute the following git command (you need git version 1.8.2+) :

git submodule update --init --remote


First, install mod2c using the instructions provided here. Make sure to install mod2c and CoreNEURON in the same installation directory (using CMAKE_INSTALL_PREFIX).

Set the appropriate MPI wrappers for the C and C++ compilers, e.g.:

export CC=mpicc
export CXX=mpicxx

If you don't have MPI, you can disable MPI dependency using the CMake option -DENABLE_MPI=OFF:

export CC=gcc
export CXX=g++
About MOD files

The workflow for building CoreNEURON is different from that of NEURON, especially considering the use of nrnivmodl. Currently we do not provide nrnivmodl for CoreNEURON. If you have MOD files from a NEURON model, you have to explicitly specify those MOD file directory paths during CoreNEURON build using the -DADDITIONAL_MECHPATH option:

cmake .. -DADDITIONAL_MECHPATH="/path/of/mod/files/directory/"

This directory should have only mod files that are compatible with CoreNEURON. You can also provide multiple directories separated by a semicolon:


Building with GPU support

CoreNEURON has support for GPUs using the OpenACC programming model when enabled with -DENABLE_OPENACC=ON. Below are the steps to compile with PGI compiler:

module purge
module purge all
module load pgi/18.4 cuda/9.0.176 cmake/3.5  #change pgi and cuda modules

export CC=mpicc
export CXX=mpicxx


Note that the CUDA Toolkit version should be compatible with PGI compiler installed on your system. Otherwise you have to add extra C/C++ flags. For example, if we are using CUDA Toolkit 9.0 installation but PGI default target is CUDA 8.0 then we have to add :

-DCMAKE_C_FLAGS:STRING="-O2 -ta=tesla:cuda9.0" -DCMAKE_CXX_FLAGS:STRING="-O2 -ta=tesla:cuda9.0"

If there are large functions / procedures in MOD file that are not inlined by compiler, one can pass additional c/c++ compiler flags:


CoreNEURON uses the Random123 library written in CUDA. If you are not using NrnRandom123 in your model and have issues with CUDA compilation/linking (or CUDA Toolkit is not installed), you can disable the CUDA dependency using the CMake option -DENABLE_CUDA_MODULES=OFF :


You have to run GPU executable with the --gpu or -gpu option as:

mpirun -n 1 ./bin/coreneuron_exec -d ../tests/integration/ring -mpi -e 100 --gpu

Make sure to enable cell re-ordering mechanism to improve GPU performance using --cell_permute option (permutation types : 1 or 2):

mpirun -n 1 ./bin/coreneuron_exec -d ../tests/integration/ring -mpi -e 100 --gpu --cell_permute 2

Note that if your model is using Random123 random number generator, you can't use same executable for CPU and GPU runs. We suggest to build separate executable for CPU and GPU simulations. This will be fixed in future releases.

Building on Cray System

On a Cray system the user has to provide the path to the MPI library as follows:

export CC=`which cc`
export CXX=`which CC`

We have tested the build process on the following platforms:

  • Blue Gene/Q: XLC/GCC
  • x86: Intel, PGI, GCC, Cray
  • OS X: Clang, GCC

Optimization Flags

  • One can specify C/C++ optimization flags specific to the compiler and architecture with -DCMAKE_CXX_FLAGS and -DCMAKE_C_FLAGS options to the CMake command. For example, on a BG-Q:
cmake .. -DCMAKE_CXX_FLAGS="-O3 -qtune=qp -qarch=qp -q64 -qhot=simd -qsmp -qthreaded" -DCMAKE_C_FLAGS="-O3 -qtune=qp -qarch=qp -q64 -qhot=simd -qsmp -qthreaded"
  • By default OpenMP threading is enabled. You can disable it with -DCORENEURON_OPENMP=OFF
  • By default CoreNEURON uses the SoA (Structure of Array) memory layout for all data structures. You can switch to AoS using -DENABLE_SOA=OFF.
  • If the default compiler flags are not supported, try -DCMAKE_BUILD_TARGET=SOME_TARGET


Note that the CoreNEURON simulator dependends on NEURON to build the network model: see NEURON documentation for more information. Once you build the model using NEURON, you can launch CoreNEURON on the same or different machine by:

export OMP_NUM_THREADS=8     #set appropriate value
mpiexec -np 2 /path/to/isntall/directory/coreneuron_exec -e 10 -d /path/to/model/built/by/neuron -mpi

This tutorial provide more information for parallel runs and performance comparison.

In order to see the command line options, you can use:

/path/to/isntall/directory/coreneuron_exec --help
-b, --spikebuf ARG       Spike buffer size. (100000)
-c, --threading          Parallel threads. The default is serial threads.
-d, --datpath ARG        Path containing CoreNeuron data files. (.)
-dt, --dt ARG            Fixed time step. The default value is set by
                         defaults.dat or is 0.025.
-e, --tstop ARG          Stop time (ms). (100)
-f, --filesdat ARG       Name for the distribution file. (files.dat)
-g, --prcellgid ARG      Output prcellstate information for the gid NUMBER.
-gpu, --gpu              Enable use of GPUs. The default implies cpu only run.
-h, --help               Print a usage message briefly summarizing these
                         command-line options, then exit.
-i, --dt_io ARG          Dt of I/O. (0.1)
-k, --forwardskip ARG    Forwardskip to TIME
-l, --celsius ARG        Temperature in degC. The default value is set in
                         defaults.dat or else is 34.0.
-mpi                     Enable MPI. In order to initialize MPI environment this
                         argument must be specified.
-o, --outpath ARG        Path to place output data files. (.)
-p, --pattern ARG        Apply patternstim using the specified spike file.
-R, --cell-permute ARG   Cell permutation, 0 No; 1 optimise node adjacency; 2
                         optimize parent adjacency. (1)
-r, --report ARG         Enable voltage report (0 for disable, 1 for soma, 2 for
                         full compartment).
-s, --tstart ARG         Start time (ms). (0)
-v, --voltage ARG        Initial voltage used for nrn_finitialize(1, v_init). If
                         1000, then nrn_finitialize(0,...). (-65.)
-W, --nwarp ARG          Number of warps to balance. (0)
-w, --dt_report ARG      Dt for soma reports (using ReportingLib). (0.1)
-x, --extracon ARG       Number of extra random connections in each thread to
                         other duplicate models (int).
-z, --multiple ARG       Model duplication factor. Model size is normal size *
--binqueue               Use bin queue.
--mindelay ARG           Maximum integration interval (likely reduced by minimum
                         NetCon delay). (10)
--ms-phases ARG          Number of multisend phases, 1 or 2. (2)
--ms-subintervals ARG    Number of multisend subintervals, 1 or 2. (2)
--multisend              Use Multisend spike exchange instead of Allgather.
--read-config ARG        Read configuration file filename.
--show                   Print args.
--spkcompress ARG        Spike compression. Up to ARG are exchanged during
                         MPI_Allgather. (0)
--write-config ARG       Write configuration file filename.

Default values for all parameters are printed by rank 0 on launch. E.g.

$ cpu/bin/coreneuron_exec --show

--spikebuf = 100000      --spkcompress = 0        --prcellgid = -1
--cell-permute = 1       --nwarp = 0              --ms-subintervals = 2
--ms-phases = 2          --report = 0             --multiple = 1
--extracon = 0           --pattern = not set      --datpath = .
--filesdat = files.dat   --outpath = .            --write-config = not set
--read-config = not set  --tstart = 0             --tstop = 100
--dt = -1000             --dt_io = 0.1            --voltage = -65
--celsius = -1000        --forwardskip = 0        --dt_report = 0.1
--mindelay = 10          --help = not set         --threading = not set
--gpu = not set          -mpi = not set           --show = set
--multisend = not set    --binqueue = not set


Note that celsius and dt, if not specified, will get their values from the models /defaults.dat file.


Currently CoreNEURON only outputs spike data. Spike output file need to be sorted to compare with NEURON:

sort -k 1n,1n -k 2n,2n out.dat > out.spk

Running tests

Once you compile CoreNEURON, unit tests and a ring test will be compiled if Boost is available. If you pass the path for Neurodamus channels, 10 cell tests will also be compile. You can run tests using

make test

If you have different mpi launcher, you can specify it during cmake configuration as:


Developer Notes

If you have installed clang-format, you can reformat/reindent generated .c files from mod2c using:

make formatbuild

The .clang-format file in the source repository is compatible with version 5.0.


  • See LICENSE.txt
  • See NEURON
  • The mechanisms and test datasets appearing in the CoreNeuron repository are subject to separate licenses. More information is available on the NMC portal website NMC portal, the specific licenses are described in the ME-type model packages downloadable from that website.


To facilitate the future distributions of the software the Blue Brain Project wishes to remain the sole owner of the copyright. Therefore we will ask contributors to not modify the existing copyright. Contributors will however be gratefully acknowledged in the corresponding CREDIT.txt file.


CoreNEURON is developed in a joint collaboration between the Blue Brain Project and Yale University. Financial support was provided by the ETH Board funding to the Blue Brain Project and by the following grants: European Union Seventh Framework Program (FP7/2007-2013) under grant agreement no. 604102 (HBP), European Union’s Horizon 2020 research and innovation programme under grant agreements no. 720270, 785907 (HBP SGA1, HBP SGA2) and NIH grant number R01NS11613.