This replaces the CMake templates provided by TBB with a much more sane alternative!

The TBB CMake templates had a very strange workflow, that involved downloading the TBB source and compiling it, which made it impossible to configure the TBB build, and caused problems on systems without connection to the internet.

We replace this with a fork of the TBB repository maintained by Github user @wjakob:
https://github.com/wjakob/tbb
This fork provides a sane CMakeLists.txt that can be configured from our CMake setup.
It is added as a git submodule, so it can be downloaded with the rest of the repository, hence not requiring connection to the internet during CMake configuration.

It could be extended to use a user-provided build of TBB to use instead of building it.

fixes #332.

Ben Cumming authored 7 years ago and Sam Yates committed 7 years ago

* Rename `miniapps` subdirectory to `example`.
* Have all example executables be built under `example` in the build directory.
* Update Travis CI to run miniapp from new path.

Ben Cumming authored 7 years ago and Sam Yates committed 7 years ago

* Add three new mechanisms: `nax.mod`, `kdrmt.mod` and `kamt.mod`.
* Add new built-in math operators to `modcc`: `min`, `max`, `abs` and `exprelr`. `exprelr` is defined as the reciprocal of the 'exprel' function, exprel(x)=x/(exp(x)-1), exprel(1)=1. This function occurs frequently in HH-style mechanisms, and having a built-in operator avoids the ad hoc `vtrap` functions found in NMODL files in the wild.
* Split Arbor SIMD intrinsics support into AVX2- and AVX512-specific files.
* Add unit tests for new maths operators for C++, SIMD and CUDA implementations.

Restructure the miniapp in such a way that we have to option to have multiple parallel mini-applications.

Move the original miniapp directory to a miniapps directory.
Output executable also in a nested miniapps directory.
Update the Travis to point to the new executable location.

* Remove optimization option (use SIMD options for vectorization).
* Remove arbor utility library dependencies from modcc (pending separation of utility lib from arbor lib source).
* Split target (cpu, gpu) specification from vectorization architecture (avx2, avx512).
* Remove `Options` singleton; replace with structure local to `modcc.cpp`.
* Tidy `modcc` option parsing and main function; allow a single invocation of `modcc` to generate code for multiple backends.
* Rename generated sources to include backend target in filename.
* Always run a constant simplification pass on generated procedures.
* Remove file i/o code from `Module` and `modcc` main function; move functionality to new functions in `io` namespace. (Note: in on-going mechanism revamp, other i/o utility code will reside in the `io` namespace and subdirectory.)
* Remove classes `ConstantFolderVisitor` and `ExpressionClassifierVisitor` that are no longer used.
* Modify CMakeLists.txt files, `backends/*/fvm.cpp` to reflect the new filenames of generated sources.
* Small formatting changes in `modcc` source to reflect coding guidelines (incomplete).

* Use ARB_ and arb_ as variable prefixes in place of NMC_ and nmc_.
* Replace references to 'NestMC' and 'NEST MC' to refer instead to Arbor.
* Use 'arbor' as the sim name in generated validation data.
* Reflow long-line paragraphs in `tests/ubench/README.md`.
* Change names of CUDA mechanism and CUDA kernel libraries to include arbor name.

Ben Cumming authored 7 years ago and Sam Yates committed 7 years ago

Separable compilation of the CUDA kernels generated by modcc from NMODL files.

CMake scripts:
* Update the `build_modules()` helper function to cleanly handle calls to modcc that generate multiple output files.
* Add a new library target `gpu_mechanisms` for the separately compiled CUDA kernels and the implementation of their C wrappers.
* Reduce verbosity of compilation messages.

* Simplify mechanism C++ namespace use: move everything in nest::mc::mechanisms::gpu::_mechanism-name_ into `nest::mc::gpu`, and similarly for multicore mechanism implementations, ions.
* Remove template parameters for `value_type` and `size_type` from all of the 
mechanism implementations, and use `fvm_value_type` and `fvm_size_type` everywhere instead.

modcc changes:
* Modify `CUDAPrinter` to keep track of 3 text buffers, one each for 
  "implementation", "interface" and "implementation interface":
* Write the CUDA implementation interface to `X_impl.hpp`, comprising the definition of the mechanism-specific 'X_ParamParck' struct used to pass function arguments to the CUDA kernels.
* Write the CUDA kernels and C wrappers to `X_impl.cu`.
* Write the public C++ mechanism interface (with calls to implementation wrappers) to `X.hpp`.
* Modify modcc driver to support multiple generated output files.

Ben Cumming authored 7 years ago and Sam Yates committed 7 years ago

Refactor the threshold_watcher and stack data structures in the gpu backend so that they are amenable to separable compilation.

* Make `gpu::stack<T>` have a host-only interface that wraps a POD type `gpu::stack_base<T>`.
* Implement a `push_back(stack_base, value)` method in `backends/gpu/kernels/stack.hpp` that is visible only to device code.
* Move `test_thresholds` kernel to a .cu file, replacing template parameters with types provided by `backends/fvm_types.hpp`.
* Add a simple C function interface, callable from host side code, defined in `backends/gpu/threshold_common.hpp`.
* Simplify the `gpu::impl::padded_size` function (both to read and in terms of efficiency).
* Use `typeid` as the default for pretty-printing types in the memory back end.
* Update the `test_gpu_stack` unit test to support new gpu stack interface.
* Fix bug in the `test_spikes` unit test, which was not running the GPU back end in the cuda unit tests.

Add support for continuous integration with Travis CI.
This implements bare bones support that can be extended over time.

Travis CI test environments:

    All use gcc 5.
    Test the serial distributed back end with serial and cthread threading backends.
    Test mpi with cthread.
    The tbb test failed sporadically because CMake, so it is disabled for now.

The test script:

    Builds the unit tests, global_communication tests and miniapp.
    Asserts that all unit and global_communication tests pass.
    Asserts that the miniapp runs successfully.
        does not test miniapp output for now.

There is plenty of scope for improving the tests.
A key improvement will be to use validated output for the validation and miniapp
to provide some validation.

There were some small fixes required to make the tests pass on Travis

    communication/mpi.hpp now sets default size and rank values of 1 and 0 respectively
    to allow all unit tests to pass when built with MPI.
    The wrappers around MPI API calls use const_cast to support MPI implementations that
    are not "const aware".
    A missing header was added to tests/unit/test_range to make std::unordered_multimap
    available.`

Ben Cumming authored 7 years ago and Sam Yates committed 7 years ago

Adds support for building documentation with Sphinx from reStructuredText-formatted files in the `doc` subdirectory. Automatic building has been verified with ReadTheDocs.

* Add basic documentation to the `doc` path.
* Use a git submodule and associated CMake to pull in ReadTheDocs theme at configuration time.

Ben Cumming authored 7 years ago and Sam Yates committed 7 years ago

* Add support for CMake scripts provided by TBB.
* Update required cmake version to 3.0.

* hack to get linking to work on Cray PE

* improve comments and remove redundant include in CMakeLists

* firewall the tbb cmake files

* tbb threading back end to_string includes version number

Adds a new AVX512 target for processors supporting only the core AVX512 functionality, which currently means SkyLake Xeon processors.

Ben Cumming authored 7 years ago and Sam Yates committed 7 years ago

Fixes #266.

Use CUDA to compile the `cell_group_factory` so that the CUDA back end is compiled correctly, instead of the null back end proxy.
  * Added bonus: the miniapp is now compiled using host C++ compiler instead of `nvcc`.

This is a little bit hacky, because this is a stop gap until we have separate compilation of CUDA code.

Ben Cumming authored 7 years ago and Sam Yates committed 7 years ago

Fixes #190.

The final piece in the metering features.

* Add a `power_meter` which currently records energy used on each node of a Cray XC{30,40,50} systems, which all have built in `pm_counters` interface to power measurement.
* Add information about which node each MPI rank runs on to the metering output in `meters.json`, which is needed to analyse energy recordings, which are per node, not per MPI rank.
* Refactor collation of measurements: now the responsibility of the meter manager.
* Add support for `gather` with `std::string` to the global communication policy, which required a back end MPI implementation and corresponding unit test.
* Add `src/util/config.hpp` that populate the `nest::mc::config` namespace with `constexpr bool` flags describing system or environment capabilities.

Ben Cumming authored 8 years ago and Sam Yates committed 8 years ago

Fixes #212.

* Update the main `CMakeLists.txt` file to select the cthread back end by default, and present the threading options in the order: cthread, tbb, serial.

Ben Cumming authored 8 years ago and Sam Yates committed 8 years ago

Fixes #152

* Remove OpenMP back end implementation.
* Remove CMake options for OpenMP.
* Simplify the threading model selection code in CMake.
* Remove Extrae benchmarking scripts, which require OpenMP.

Basic features:

* Compile with -t avx512
* Automatically set up by CMake if USE_OPTIMIZED_KERNELS is on and VECTORIZE_TARGET is set to KNL 
* Generic SIMD printer that contacts a SIMD backend for emitting the actual SIMD intrinsics

Note: compilation for the avx512 target requires the Intel compiler. 

Ben Cumming authored 8 years ago and Sam Yates committed 8 years ago

Fixes #125

* Add `cuda_atomic_add` and `cuda_atomic_sub` wrappers for atomic addition.
* Choose native atomic add for Pascal and later architectures.
* Choose CAS workaround for devices earlier than Pascal.
* Add unit test for wrappers.
* Change default CUDA architecture target to `sm_60` in `CMakeLists.txt`.

Ben Cumming authored 8 years ago and Sam Yates committed 8 years ago

Moves spike detection to the back end, which is required to have fast spike detection on the gpu.

Fixes #106.

Backend:
* Move spike detection into the backend.
* Add a `threshold_watcher` type to each backend that is initialized with a reference to the field that it is to watch, along with indexes and thresholds for each variable in the field that is being watched. This class presents a simple host-side interface:
   * `test(t)` tests for crossings at time `t`.
   *  `crossings()` returns all threshold crossings.
   * `clear_crossings()` resets (clears) the collected crossing events.
* Implement the multicore back end detector directly from the original code.
* Implement a `gpu_stack` for use with the gpu back end, that lets threads in a kernel conditionally push back into a flat array.

Miniapp:
* Run a single-step dummy run of model before starting the profiler, when profiling is enabled.
* Initialize the spike output callback functions _after_ the dummy run so that spikes from the dummy step are not output.

`cell_group`:
* Pass responsibility for spike detection to the lowered cells (`fvm_multicell`) and associated back ends.

`memory`:
* Add a new allocator for CUDA managed memory.
* Implement `managed_ptr` and `make_managed_ptr`, which are managed memory equivalents of `std::unique_ptr` and `std::make_unique_ptr`.

Tests:
* Improve host-side spike detection unit tests.
* Add device-side spike detection unit tests.
* Add unit tests for `gpu_stack`.

Building:
* Surpress CMP0023 CMake warning.

Adds a stand-alone program for the generation of random morphologies form a L-system description. The algorithm is that of Burke (1992), with some of the extensions provided by Ascoli et al. (2001).

Two sets of L-system parameters have been included, corresponding to alpha motoneurons and Purkinje cells, but there is certainly something wrong with the data for the latter, and more correct numbers will probably need to be synthesized from existing Purkinje cell morphological information.

Documentation for `lmorpho` is incomplete, but the command line help (`--help`) goes some way to explain the usage. In order to get output, one must specify `--swc` or `--pvec` (or both) to emit SWC files or the structural parent vectors. Coarser discretization can be obtained with the `--segment` option.

Some minor modifications have been included in other parts of the source repo:
* Added copy constructor for `TextBuffer` in `modcc/textbuffer.hpp`, required to keep cl...

Add a dry run mode, inspired by the dry run mode implemented in NEST. A dry run
of a model simulates running a large distributed model by running only the work
of one of the ranks, with artificial spike input from the other "dummy" ranks.

This is implemented as a new global communication back end, dryrun_global_policy,
the implementation of which is straightforward:

a new implementation of gather_spikes that takes the local spikes and
replicates them n times where n is the total number of simulated
ranks.
the global_policy::size() method returns the number of ranks in the
simulated run
the new back end has to store some state that records the number
of simulated ranks and cells per rank, which are set using the new
global_policy::set_sizes() method
Some CMake modificatins were required:

make the selection of the global communication backend have the same
interface as that for selecting the threading back end.
small improvements to the selection of the threa...

Alexander Peyser authored 8 years ago and Sam Yates committed 8 years ago

Add threading pool built on `std::thread`

* Provide new threading model 'cthread' for nestmc based on a pool of `std::thread` objects.
* Unify duplicated timer class provided by `serial`, `omp` and now `cthread` threading models.

Remove redundant MPI set

* Fix CMakeLists to handle build as a subproject

When several CMake generated projects are build together, it is common
practice to have a 'superproject' CMakeLists that uses
  add_subdir(proj1)
  add_subdir(proj2)
  ...
where each subproject is a self contained CMake based project
(Example proj1=HPX, proj2=nestmc, proj3=another, ...)

CMAKE_SOURCE_DIR always points to the top level directory which
is the superproject dir in this case, whereas PROJECT_SOURCE_DIR
always points to the root of the current project() in the CMakeLists
so one shouod use PROJECT_SOURCE_DIR as this gets the relative paths
correct.

* Add option to turn off auto generation from *.mod files

* Fix #134 : Change CMake WITH_OPTION to NMC_WITH_OPTION, compiler #define to NMC_HAVE_OPTION

1) The user may select an option by saying NMC_WITH_XXX

2) This may trigger CMake to use find_package(...) or setup some
other variables. CMake can then set variable NMC_HAVE_XXX and add a
what has actually been used.

3) Code should use #ifdef NMC_HAVE_XXX to check for a feature

Old CMake/define      New CMake                 Compiler #define
----------------      ---------                 ----------------
THREADING_MODEL       NMC_THREAD_MODEL
    WITH_TBB          NMC_WITH_TBB              NMC_HAVE_TBB
    WITH_OMP          NMC_WITH_OMP              NMC_HAVE_OMP
    WITH_SERIAL       NMC_WITH_SERiAL           NMC_HAVE_SERIAL

WITH_MPI              NMC_WITH_MPI              NMC_HAVE_MPI
WITH_CUDA             NMC_WITH_CUDA             NMC_HAVE_CUDA
WITH_GPU                                        NMC_HAVE_GPU
WITH_ASSERTIONS       NMC_WITH_ASSERTIONS       NMC_HAVE_ASSERTIONS
WITH_TRACE            NMC_WITH_TRACE            NMC_HAVE_TRACE
WITH_PROFILING        NMC_WITH_PROFILING        NMC_HAVE_PROFILING

Other user visible CMake vars
-----------------------------
VECTORIZE_TARGET            -> NMC_VECTORIZE_TARGET
USE_OPTIIZED_KERNELS        -> NMC_USE_OPTIIZED_KERNELS
BUILD_VALIDATION_DATA       -> NMC_BUILD_VALIDATION_DATA
BUILD_JULIA_VALIDATION_DATA -> NMC_BUILD_JULIA_VALIDATION_DATA
BUILD_NRN_VALIDATION_DATA   -> NMC_BUILD_NRN_VALIDATION_DATA
VALIDATION_DATA_DIR         -> NMC_VALIDATION_DATA_DIR

Variables such as NMC_THREADING_MODEL and NMC_VECTORIZE_TARGET now use
enumerated cmake values so you can toggle between them in ccmake gui.
SYSTEM_TYPE_CRAY/BGQ        -> NMC_SYSTEM_TYPE (Generic/Cray/BGQ)

* Use generator expression for modcc path

Some IDE's (like Xcode for example), override the CMake binary paths
and add /Debug or /Release etc so rules that have hard coded paths
to binaries will fail.

Vasileios Karakasis authored 8 years ago and Sam Yates committed 8 years ago

These tests are intended to test the sanity of the `modcc` generated code for the individual mechanisms. The don't have any physical background. Potentially optimized CPU-targeted mechanisms generated in the build are compared with unoptimized mechanisms generated from the reference modules.

* Add generic unit tests for individual mechanisms.
* Make unit tests exercise potential problems with aliased indexes (point processes).
* Ensure unit tests correspond to multiple low level vector operations.
* Ensure unit tests run with voltage, current and indices initialized with varying values.
* Refactor CMake code for module compilation to reduce cut-and-paste code and build complexity.

Compiles on bgq

define MPICH2_CONST const for BGQ

Add SYSTEM_BGQ to cmake to handle mpi headers

This PR is part of the gpu feature merge. The GPU implementation is not implemented here. Instead, we focus on refactoring of the original "multicore" back end so that it is ready for adding the GPU back end.

This is a big and messy change, for which I am sorry.

## build System

- A `WITH_CUDA` option has been added to the main CMakeLists. This finds the CUDA toolkit, and sets CUDA compiler flags, and will build unit tests for the gpu back end.
- The CMakeLists that generates mechanisms with modcc has been updated to generate CUDA mechanisms.
- the library is now named `libnestmc` instead of `libcellalgo`
- merge the external libraries that are optionally linked againts (tbb, libunwind, etc) into a single
  `EXTERNAL_LIBRARIES` list for ease of linking

## modcc

- the cprinter and cudaprinter have had small changes to generate mechanism files that are compatible with the refactored library.

## algorithms

- the indexes into algorithm was "rangified". An algorithm `index_into_iterator` takes two ranges as inputs to make a range that lazily generates the index of sub into super set.

## backends

- made a new path `src/backends/` for backend specific type and implementation code.
- currently:
  - complete support for the `multicore` and `gpu` backends
  - `gpu` back end is not optimized or validated
- the back end implementations are in `src/backends`
- a single `backend` class, `nest::mc::{multicore,gpu}::backend`, is provides all backend specific type and implementation details fro each backend
  - storage containers
  - Hines matrix assembly for FVM method
  - Hines matrix solver
  - mechanism "factory"

## lowered fvm cells

- removed `fvm_cell` because this can be modelled with an `fvm_multicell` with one cell.
- refactored to use backend type and implementation from `fvm_policy`
- use `std::vector` instead of containers in `nest::mc::memory::` where possible when building cells.

## memory library

Refactor the "memory" library, making it much simpler and better integrated into the rest of the application. However, it is still far from perfect. The `Coordinator` approach needs to be improved, most likely by putting target-specific wisdom into pointers (which could obviate the need for a `const_array_view` type.
1. renaming and moving
   - move from `vector/` to `src/memory`
   - move into the `nest::mc` namespace, i.e. all types and functions are now in `nest::mc::memory`
   - change from camel case nameing scheme to NestMC style naming.
2. simplification
   - remove the CRTP cruft that was used to make operator overloading work for operations like copying from one range into another, and filling a range with a constant value. These have been replaced with `memory::fill()` and `memory::copy()` helper functions. This simplified the code _a lot_, and makes code clearer in user land.
   
   ```
   // before
   vec(0, 5) = other;
   // now
   memory::copy(other, vec(0, 5));
   ```
   - add some wrappers in `src/memory/wrappers.hpp` that help with making views. These are particularly useful for passing `std::vector` through interfaces that expect a view.

## debug backtraces

Added stack traces for debugging.
- support for OSX and Linux via libunwind
- backtraces can be generated manually `nest::mc::util::backtrace().print()`
  - creates a new file and dumps trace into file
  - prints message to `stderr` with file name and instructions on how to analyse
- backtraces are also automatically generated when an assertion `EXPECTS` statement fails
- a python script in `scripts/print_backtrace` pretty prints the output with file name, line number and demangled symbols

## util simplification and consolidation

The `src/util.hpp` file was removed
- much of its contents were dead code and just removed
- useful components like `pprintf` and `make_unique` were moved into the `src/utils` path in standalone files
There was a lot of overlap between functionality provided in `src/memory/util.hpp` and existing functions/types in the `nest::mc::util` namespace. The `memory` implementations were removed, and their `nest::mc::util` counterparts used. There is still some work remaining, namely moving the rest of the `src/memory/util.hpp` into `src/util/...`

* first version of openmp threading back end

* adding openmp parallel sort implementation

* OpenMP sort working

* Support for units syntax within state block.

* Add soma-less cable cell to test cells.

Also:
* Ensure intrinsic and passive properties properly set on test cells.

* Change bulk resistivity default.

* Align defaults with values used in most of the NEURON
  validation scripts.
* Use consistent 100 Ω·m bulk resistivity across both
  NEURON test models and basic validation cells.

* OpenMP back end working

* Add Extrae+paraver support, needs to fix compilation warnings

* Reorganize validation data generation

* Move generation and data to top-level validation directory.
* Make BUILD_VALIDATION_DATA and VALIDATION_DATA_DIR cache vars.
* Add helper CMake functions for data generation.

Note `validation/ref/numeric/foo.sh` is just a placeholder.

* Bugfix: hh_soma.jl

* Use consistent scaling for y[1] scalar voltage in hh_soma.jl
* Also: add more reserved target names to CMakeLists.txt
  helper function.

* Refactor convergence tests; add numeric soma ref.

* Amend data directory path in validation tests.
* Enmodulate `hh_soma.jl`
* Add HH channel reference data generations script.
* Switch `validate_soma.cpp` to numeric reference data.
* Consolidate common code in `validate_ball_and_stick.cpp`
* Add (nearly) Rallpack1 validation test (see below).
* Gentle failure on absence of reference data in
  `validate_ball_and_stick.cpp`

Can't yet override mechanism default parameter values,
so the cable cell model added to `test_common_cells.hpp`
lets the default stand; validation script will have
to use the default membrane conductance rather than that
given by Rallpack1.

* Add Rallpack1 validation, plus bugfix, clean

* Implement Rallpack1 validation test (with a workaround
  for inability to set membrane conductance).
* Fix bug in L≠1 case in PassiveCable.jl (this may still be
  wrong).
* Fix bug in peak delta computation in trace analysis when
  both traces have no local maxima.
* Gentle failure on missing `numeric_soma.json`
* Allow multiple `-s` selection operations for `tsplot`,
  acting disjunctively.

* Remove errant test file.

* file's cleanup

* Remove tabs

* Use correct routine in numeric_rallpack1.jl x0.3

* Configure-time test for julia

* `math::infinity<>()` wrapper for infinity

* Use name `i_e` for Stim current density

* Use `math::infinity<>()` for infinite value

* Adds unit tests for the STATE block.

* Add "lib" to search prefixes for libtbb

* Fix quoting error in library search.
* Add "lib" to prefixes when system is "Linux".

* Address deprecated use of 'symbol' warning.

Julia 0.5 deprecates use of `symbol` instead of
`Symbol`. This patch just substitutes the
correct call.

* Address deprecated use of 'symbol' warning.

Julia 0.5 deprecates use of `symbol` instead of
`Symbol`. This patch just substitutes the
correct call.

* Addresses PR comments.

* Unit tests for math.hpp

* Tests for `math::pi`, `math::lerp`, `math::area_frustrum`
  and `math::volume_frustrum`
* Fix `math:pi<long double>()`.

* Extend range, view functionality.

* New `filter` view: lazily selects based on predicate.
* Generic `front` and `back` for sequences.
* New rangeutil STL wrappers `stable_sort_by`, `all_of`, `any_of`.
* Consolidate common utility unit testing structures into
  `tests/unit/common.hpp`

* Add `ball_and_squiggle` model; fix `ball_and_taper`.

* Make `test_common_cells.hpp` and `ball_and_taper.py` agree.
* Add `ball_and_squiggle` model that has a tapering undulating
  profile.

* Address PR#46 review comments.

* Add documentation of template parameters for `filter_iterator`.
* Document use of `uninitalized<F>` for holding functional objects
  in `filter_iterator` and `transform_iterator`

* Consolidate validation test code (issue #41)

* Simplify trace analysis and reporting code in
  `trace_analysis.hpp`
* Consolidate convergence test run procedures into
  new class `convergence_test_runner`.

* New compartment info structure for FVM.

* Make `algorithm::sum`, `algorithm::mean` more generic,
  allowing use with array types.
* Add `div_compartment` compartment representation, that
  holds geometric information for each half of a compartment
  that will then be used in calculating control volumes.
* Add three compartmentalisation schemes/policies that
  discretize a segment into `div_compartment` objects:
    * `div_compartment_by_ends` divides based only on the
      segment end points and radii.
    * `div_compartment_sampler` forms frusta by sampling
      the segment radius at each compartment boundary
    * `div_compartment_integrator` computes the compartment
      areas and volumes exactly by summing all frustra
      in the intersection of the segment and the compartmnet
      span.

* Extrae linked at execution time

* cleaning project

* Complex compartments

* Use divided compartments to determine FVM coefficients.
* Pick correct control volume in FVM from sgement position (avoids
  off-by-half error.)
* Add colour override functionality to tsplot: `--colour` option.
* Add const accessor for cell soma.
* Source formatting, comments in `math.hpp`
* Fix `range_view`: was using incorrectly named type trait.
* Add unit test for `range_view`.
* Allow points of discontinuity to be omitted from L-infinity norm
  calculations.
* Add `-d, --min-dt` option to `validate.exe` to control time
  step in validation convergence tests.
* Add validation test: confirm divided compartment policy does
  not effect results on simple frustrum dendrites.
* Change default max compartments on validation tests to 100
  (ad hoc observed convergence limit at dt circa 0.001 ms;
  finder spatial division would required much finer dt.)
* Make NEURON validation data generation scripts use CVODE by
  default, and with `secondorder=2` when non-zero `dt` is given.

* Remove division policy type parameter.

* Use only `div_compartment_integrator` for compartmentalization in
  `fvm_multicell`. The policy will later be moved to a backend
  policy class.
* For now, disable validation tests that test different division
  policies (see above).
* Tweak comments and remove redundant `using`, following comments
  on PR#54.

* Minor twicks and corrections

* Move generation and data to top-level validation directory.
* Make BUILD_VALIDATION_DATA and VALIDATION_DATA_DIR cache vars.
* Add helper CMake functions for data generation.

Note `validation/ref/numeric/foo.sh` is just a placeholder.

Validation of simulation results by comparing L-infinity distance and maximum peak displacement in voltage traces taken at mid-points and end-points of sections.

Note that these tests will broadly _fail_ at this point.

Reference data generation and visualization:
* Use voltage traces as validation data from NEURON; refactor generation scripts.
* Generate validation data as a dependency of `validation.exe`.
* Store validation data in a `tsplot`-compatible format.
* Extend `tsplot` to handle multiple time series per file, a non-time 'time' axis (see `-A` option), filtering of time series by meta data queries (see `-s` option).
* Remove pre-generated spike-time validation data files.

Core extensions:
* Add a single-cell `singleton_recipe` recipe wrapper.
* Allow cell descriptions to be cloned (explicitly) for use with this wrapper.
* Add `simple_sampler` which maintains a trace of scalar observables as a vector of (time, value) pairs.
* Allow cell groups to be exposed from `model` (used for post-synaptic event injection in synapse validation test.)

Utility extensions:
* Add `math::signum` function.
* Fix `value_type` determination in `util::transform_iterator` where the underlying iterator dereferences to a reference type.
* Add `util::max_element_by` and `util::max_value` sequence utilities to `rangeutil.hpp`.
* Small bug fixes for `util::optional` (one const correctness case, and proper behaviour for implicit conversion of `nothing_t` to `optional<void>`.)
* Generic `util::first` and `util::second` accessor functional objects for reference access to `std::pair` fields in the absence of generic lambda functions.
* Add `util::path` for path manipulation, corresponding to a subset of C++17 `std::filesystem::path` functionality. Only POSIX path semantics supported at this point.

Validation tests:
* Rework all validation tests as comparisons of voltage trace data against a (presumably converged) reference trace generated by NEURON.
* Add options to `validation.exe` driver for verbose output of test results (`-v`), limiting the compartment number in convergence tests (`-m`) and saving the generated traces to a `tsplot`-compatilble JSONfile (`-o`).
* Gather trace comparison metrics and analysis into `trace_analysis.hpp` and `trace_analysis.cpp`.
* Add super simple command line argument parsing utility `tinyopt.hpp`.
* Make a consistent naming of `ball_and_3stick` model across sources.
* New `ball_and_taper` model.

* update the out of date version of modparser was added to the repository
* fix some warnings about unused static functions in a modcc test header
* move modcc/src path contents to modcc, because there was little point having
  the additional sub directory.

* only the source has been moved over and the cmake rules updated
* the tests still have to be moved

* fix compile time error in src/model.hpp
* add mpi_listener type for sensible output and error reporting
  when using MPI with Google Test.
* add stub for communicator unit testing

* the user can specify one of {none,AVX,AVX2,KNL} as
  targets for vectorization
* if modcc is available in PATH it will be used, which
  makes cross compilation easier
* a new flag USE_OPTIMIZED_KERNELS can be set to
  generate optimized kernels from the modcc compiler
  (equivalent to adding -O flag to modcc)