# Build system¶

Elemental’s build system relies on CMake in order to manage a large number of configuration options in a platform-independent manner; it can be easily configured to build on Linux and Unix environments (including Darwin), as well as via Cygwin in a Windows environment (Visual Studio support will be re-enabled in the near future). A relatively recent C++11 compiler (e.g., gcc >= 4.8) is required in all cases (please see libelemental.org/compilers/ for information on supported toolchains, and please feel free to provide feedback as/if this information becomes out-of-date).

Elemental’s main external dependencies are

1. CMake ,
2. MPI ,
3. BLAS ,
4. LAPACK,
5. METIS, and
6. PMRRR,

and the dependencies which can not currently be automatically handled by Elemental’s build system are

1. CMake, and
2. MPI.

Ubuntu users may want to install Elemental from the Ubuntu PPA.

## Handling mandatory external dependencies¶

### Installing CMake¶

Elemental uses several relatively new CMake modules, so it is important to ensure that CMake version 2.8.12 or later is available. Thankfully, the installation process is extremely straightforward: either download a platform-specific binary from the downloads page, or instead grab the most recent stable tarball and have CMake bootstrap itself. In the simplest case, the bootstrap process is as simple as running the following commands:

./bootstrap
make
sudo make install


Note that recent versions of Ubuntu (e.g., version 13.10) have sufficiently up-to-date versions of CMake, and so the following command is sufficient for installation:

sudo apt-get install cmake


If you do install from source, there are two important issues to consider

1. By default, make install attempts a system-wide installation (e.g., into /usr/bin) and will likely require administrative privileges. A different installation folder may be specified with the --prefix option to the bootstrap script, e.g.,:

./bootstrap --prefix=/home/your_username
make
make install


Afterwards, it is a good idea to make sure that the environment variable PATH includes the bin subdirectory of the installation folder, e.g., /home/your_username/bin.

2. Some highly optimizing compilers will not correctly build CMake, but the GNU compilers nearly always work. You can specify which compilers to use by setting the environment variables CC and CXX to the full paths to your preferred C and C++ compilers before running the bootstrap script.

#### Basic usage¶

Though many configuration utilities, like autoconf, are designed such that the user need only invoke ./configure && make && sudo make install from the top-level source directory, CMake targets out-of-source builds, which is to say that the build process occurs away from the source code. The out-of-source build approach is ideal for projects that offer several different build modes, as each version of the project can be built in a separate folder.

A common approach is to create a folder named build in the top-level of the source directory and to invoke CMake from within it:

mkdir build
cd build
cmake ..


The last line calls the command line version of CMake, cmake, and tells it that it should look in the parent directory for the configuration instructions, which should be in a file named CMakeLists.txt. Users that would prefer a graphical interface from the terminal (through curses) should instead use ccmake (on Unix platforms) or CMakeSetup (on Windows platforms). In addition, a GUI version is available through cmake-gui.

Though running make clean will remove all files generated from running make, it will not remove configuration files. Thus, the best approach for completely cleaning a build is to remove the entire build folder. On *nix machines, this is most easily accomplished with:

cd ..
rm -rf build/


This is perhaps a safer habit than simply running rm -rf * since, if accidentally run from the wrong directory, deleting build/ would be unlikely to have any effect.

### Installing MPI¶

An implementation of the Message Passing Interface (MPI) is required for building Elemental. The two most commonly used implementations are

1. MPICH,
2. OpenMPI, and
3. MVAPICH,

where MVAPICH is primarily focused on systems with InfiniBand and/or GPUs.

Each of the respective websites contains installation instructions, but, on recent versions of Ubuntu, MPICH2 can be installed with

sudo apt-get install libmpich2-dev


and OpenMPI can be installed with

sudo apt-get install libopenmpi-dev


wget http://www.mpich.org/static/downloads/3.2/mpich-3.2.tar.gz
tar -xzf mpich-3.2.tar.gz
cd mpich-3.2/
./configure --prefix=/where/to/install/mpich --CC=YourCCompiler --CXX=YourC++Compiler --FC=YourFortranCompiler
make
sudo make install


where the sudo is obviously not needed if you have permission to install files into the directory specified with --prefix. Lastly, these instructions assumed the existence of a Fortran compiler, and so, if one is not available, you should instead run the commands:

wget http://www.mpich.org/static/downloads/3.2/mpich-3.2.tar.gz
tar -xzf mpich-3.2.tar.gz
cd mpich-3.2/
./configure --prefix=/where/to/install/mpich --CC=YourCCompiler --CXX=YourC++Compiler --disable-fortran
make
sudo make install


Note

As noted in Issue #200, on recent versions of OS X clang does not properly build the official release of MPICH 3.2, and so it is necessary to build the most recent git revision from source.

## Soft dependencies¶

As was already mentioned, Elemental has several external dependencies which can be optionally be handled by the build process, and one (PMRRR), which is always built by Elemental. For the optionally-specified dependencies (i.e., BLAS, LAPACK, METIS, ParMETIS, and ScaLAPACK), if custom implementations were not specified during the CMake configuration phase, then appropriate libraries will be automatically downloaded/built/installed via CMake’s ExternalProject functionality. In particular, Elemental can automatically fulfill dependencies using:

1. OpenBLAS or BLIS (to provide BLAS+LAPACK)
2. METIS and/or ParMETIS (for computing a vertex separator of a graph), and
3. ScaLAPACK (for implementations of distributed Hessenberg QR algorithms).

Furthermore, there are several further (optional) external dependencies:

1. libFLAME is recommended for faster SVD’s due to its high-performance bidiagonal QR algorithm implementation,
3. Qt5 for C++11 matrix visualization,
4. matplotlib for Python matrix visualization,
5. NetworkX for Python graph visualization, and
6. NumPy for supporting the Python interface in general.

Support is not required for any of these libraries, but each is helpful for particular components of Elemental’s functionality.

### Installing BLAS and LAPACK¶

The Basic Linear Algebra Subprograms (BLAS) and Linear Algebra PACKage (LAPACK) are both used heavily within Elemental. On most installations of Ubuntu, either of the following command should suffice for their installation:

sudo apt-get install libopenblas-dev
sudo apt-get install libatlas-dev liblapack-dev


The reference implementation of LAPACK can be found at

and the reference implementation of BLAS can be found at

However, it is better to install an optimized version of these libraries, especialy for the BLAS. The most commonly used open-source versions the BLAS are ATLAS, OpenBLAS, and BLIS. If no version of BLAS+LAPACK is detected, Elemental attempts to download and install OpenBLAS (or BLIS).

#### OpenBLAS¶

OpenBLAS is a high-performance implementation of the BLAS (and, to a somewhat lesser degree, LAPACK) which Elemental defaults to downloading and installing if no other high-performance implementation was detected . For example, by default, on Mac OS X, either Accelerate or vecLib is used, but this behavior may be overridden via the CMake option -D EL_PREFER_OPENBLAS=TRUE. Furthermore, Elemental may be requested not to use OpenBLAS via the option -D EL_DISABLE_OPENBLAS=TRUE. Lastly, while Elemental will, by default, search for a previous installation of OpenBLAS before attempting to download and install the library, this search can be prevented via the -D EL_BUILD_OPENBLAS=TRUE option.

#### BLIS¶

BLIS is “a software framework for instantiating high-performance BLAS-like dense linear algebra libraries” and can optionally be downloaded and installed as part of Elemental’s build process. In order to do so on non-Apple architectures, the flag -D EL_DISABLE_OPENBLAS=TRUE should be enabled to avoid the OpenBLAS default, and, on Apple-architectures, the flag -D EL_PREFER_BLIS_LAPACK=TRUE should be specified to avoid the vecLib/Accelerate frameworks.

#### libFLAME¶

libFLAME is an open source library made available as part of the FLAME project. Elemental’s current implementation of parallel SVD is dependent upon a serial kernel for the bidiagonal SVD. A high-performance implementation of this kernel was recently introduced in [vZvdGQ2014].

Installation of libFLAME is fairly straightforward. It is recommended that you download the latest nightly snapshot from

and then installation should simply be a matter of running:

./configure
make
sudo make install


Automatic installation of libflame will hopefully be added into Elemental’s build system soon (pending the resolution of issues in the current libflame build system). Until that time, it is necessary to manually specify libflame as part of the MATH_LIBS variable. For example, if libflame is available at /path/to/libflame.a, then this library needs to be prepended to the list of BLAS and LAPACK libraries, e.g., via:

-D MATH_LIBS="/path/to/libflame.a;-L/usr/lib -llapack -lblas -lm"


or:

-D MATH_LIBS="/path/to/libflame.a;-mkl"


### PMRRR¶

PMRRR is a parallel implementation of the MRRR algorithm introduced by Inderjit Dhillon and Beresford Parlett for computing $$k$$ eigenvectors of a tridiagonal matrix of size $$n$$ in $$\mathcal{O}(nk)$$ time. PMRRR was written by Matthias Petschow and Paolo Bientinesi and, while it is included within Elemental, it is also available at:

Note that PMRRR currently requires support for pthreads.

### METIS¶

METIS is perhaps the most widely-used library for (hyper)graph partitioning and is the default tool used within Elemental in order to construct vertex separators for the Nested Dissection approach to sparse-direct factorization. In particular, Elemental makes use of the routine METIS_ComputeVertexSeparator, which is somewhat undocumented but used by ParMETIS. METIS, unlike ParMETIS, is released under the terms of the Apache License Version 2.0 (which is similar in spirit to Elemental’s New BSD License).

Support for METIS can be disabled via the CMake option -D EL_DISABLE_METIS=TRUE, or Elemental can be requested to avoid detecting a previous installation and instead immediately decide to download/install the library via the -D EL_BUILD_METIS=TRUE option.

### ParMETIS¶

ParMETIS is a parallel version of METIS that is unfortunately released under a more restrictive license that does not allow for commercial usage, and so commercial users should add the CMake option -D EL_DISABLE_PARMETIS=TRUE when configuring Elemental. Furthermore, since ParMETIS, unlike METIS, does not provide a routine for computing a vertex separator of a graph, Elemental makes use of ParMETIS’s internal APIs in order to construct such a routine (which can be viewed as a parallel analogue of METIS_ComputeVertexSeparator).

Also, Elemental can be requested to avoid detecting a previous installation (which is extremely unlikely to be sufficient due to Elemental’s usage of ParMETIS’s internal API, which is not typically installed) and instead immediately decide to download and install the library via the -D EL_BUILD_PARMETIS=TRUE option.

### ScaLAPACK¶

ScaLAPACK is the most widely-used library for distributed-memory dense linear algebra and Elemental can relatively easily interface with it should ScaLAPACK support be detected during the configuration phase of the build. While Elemental contains a relatively recent analogue of the ScaLAPACK implementations resulting from [HWD2002], [Fahey2003], and [GKK2010], this new implementation has not been properly benchmarked yet.

Support for ScaLAPACK can be enabled via the CMake option -D EL_DISABLE_SCALAPACK=OFF, and Elemental can be requested to avoid detecting previous installations and to download/install the library via -D EL_BUILD_SCALAPACK=TRUE.

If a GNU or Intel compiler is being used to compile Elemental, then it is likely that support for libquadmath was detected, and, by default, this would lead to both more robust Interior Point Methods and your copy of Elemental transitioning from the terms of the New BSD License to the GNU General Public License. If you prefer not to use libquadmath, then it can be disabled via the CMake option -D EL_DISABLE_QUAD=TRUE.

### Qt5¶

Qt is an open source cross-platform library for creating Graphical User Interfaces (GUIs) in C++. Elemental currently supports using version 5.1.1 of the library to display and save images of matrices.

Please visit Qt Project’s download page for download and installation instructions. Note that, if Elemental is launched with the -no-gui command-line option, then Qt5 will be started without GUI support. This supports using Elemental on clusters whose compute nodes do not run display servers, but PNG’s of matrices need to be created using Qt5’s simple interface.

## Getting Elemental’s source¶

There are two basic approaches:

2. Install git and check out a copy of the repository by running

git clone git://github.com/elemental/Elemental.git


## Building Elemental¶

On Unix-like machines with MPI and CMake installed in standard locations, Elemental can often be built and installed using the commands:

git clone https://github.com/elemental/Elemental
cd Elemental
mkdir build
cd build
sudo cmake ..
sudo make
sudo make install


Note that super-user privileges may be required for the cmake and make phase due to CMake’s ExternalProject_Add creating folders in the installation directory during the cmake phase and installing the external projects into the installation directory during the make phase.

As with the installation of CMake, the default install location is system-wide, e.g., /usr/local. The installation directory of the main library can be changed at any time by invoking CMake with the option:

-D CMAKE_INSTALL_PREFIX=/your/desired/install/path


and the installation of the Python interface can be switched from the default system-wide location to the user’s home directory via the option:

-D INSTALL_PYTHON_INTO_USER_SITE=ON


or instead installed into ${CMAKE_INSTALL_PREFIX}/python/ via the option: -D INSTALL_PYTHON_PACKAGE=OFF  Alternatively, the user can specify a particular directory for the python package via: -D PYTHON_SITE_PACKAGES=/your/desired/python/install/path  Though the above instructions will work on many systems, it is common to need to manually specify several build options, especially when multiple versions of libraries or several different compilers are available on your system. For instance, any C++, C, or Fortran compiler can respectively be set with the CMAKE_CXX_COMPILER, CMAKE_C_COMPILER, and CMAKE_Fortran_COMPILER variables, e.g., -D CMAKE_CXX_COMPILER=/usr/bin/g++ \ -D CMAKE_C_COMPILER=/usr/bin/gcc \ -D CMAKE_Fortran_COMPILER=/usr/bin/gfortran  and it may be necessary to manually specify the paths to the MPI compilers as well using, for example, the options: -D MPI_CXX_COMPILER=/usr/bin/mpicxx \ -D MPI_C_COMPILER=/usr/bin/mpicc \ -D MPI_Fortran_COMPILER=/usr/bin/mpif90  It is also occasionally necessary to specify which libraries need to be linked in order to link to BLAS and LAPACK (and, if SVD is important, libFLAME). The MATH_LIBS variable was introduced for this purpose and an (unrecommended for performance reasons) example for specifying BLAS and LAPACK libraries in /usr/lib might be -D MATH_LIBS="-L/usr/lib -llapack -lblas -lm"  whereas specifying Intel’s MKL libraries when using the Intel compilers is often as simple as: -D MATH_LIBS="-mkl"  It is important to ensure that if library A depends upon library B, A should be specified to the left of B; in this case, LAPACK depends upon BLAS, so -llapack is specified to the left of -lblas. If MATH_LIBS is not specified, then Elemental will attempt to download and install either OpenBLAS or BLIS, or, failing that, search for an installed reference implementation. ## Build modes¶ Elemental currently has two different build modes: • Debug - Maintains a call stack and provides significant error-checking. • Release - An optimized build suitable for production usage (assuming high-performance BLAS and MPI implementations were used) The build mode can be specified with the CMAKE_BUILD_TYPE option, e.g., -D CMAKE_BUILD_TYPE=Debug. If this option is not specified, Elemental defaults to the Release build mode. Once the build mode is selected, one might also want to manually set the optimization level of the compiler, e.g., via the CMake option -D CXX_FLAGS="-O3". Furthermore, there is also an option to attempt to make use of OpenMP parallelization when packing and unpacking MPI buffers that is enabled when the -D EL_HYBRID=TRUE CMake option is set. If this option is used, the user should ensure that a threaded BLAS implementation is used. ## Testing the C++11 installation¶ Once Elemental has been installed, it is a good idea to verify that it is functioning properly. This can be accomplished by simply running: make test  Alternatively, an example of generating a random distributed matrix, computing its Singular Value Decomposition (SVD), and checking for numerical error is available in examples/lapack_like/SVD.cpp. As you can see, the only required header is El.hpp, which must be in the include path when compiling this simple driver, SVD.cpp. If Elemental was installed in /usr/local, then /usr/local/conf/ElVars can be used to build a simple Makefile: include /usr/local/conf/ElVars SVD: SVD.cpp${CXX} ${EL_COMPILE_FLAGS}$< -o $@${EL_LINK_FLAGS} ${EL_LIBS}  As long as SVD.cpp and this Makefile are in the current directory, simply typing make should build the driver. The executable can then typically be run with a single process (generating a $$300 \times 300$$ distributed matrix, using ./SVD --height 300 --width 300  and the output should be similar to ||A||_max = 0.999997 ||A||_1 = 165.286 ||A||_oo = 164.116 ||A||_F = 173.012 ||A||_2 = 19.7823 ||A - U Sigma V^H||_max = 2.20202e-14 ||A - U Sigma V^H||_1 = 1.187e-12 ||A - U Sigma V^H||_oo = 1.17365e-12 ||A - U Sigma V^H||_F = 1.10577e-12 ||A - U Sigma V_H||_F / (max(m,n) eps ||A||_2) = 1.67825  The driver can be run with several processes using the MPI launcher provided by your MPI implementation; a typical way to run the SVD driver on eight processes would be: mpirun -np 8 ./SVD --height 300 --width 300  You can also build a wide variety of example and test drivers (unfortunately the line is a little blurred) by using the CMake options: -D EL_EXAMPLES=ON  and/or -D EL_TESTS=ON  ## Testing the Python installation¶ A number of Python example scripts which, for example, solve sparse linear systems and quadratic programs, may be found at examples/interface. However, it is typically necessary to augment the environment variable PYTHONPATH, and perhaps also LD_LIBRARY_PATH. ### Linux systems¶ On most Linux systems, it will be necessary to append $(CMAKE_INSTALL_PREFIX)/lib to LD_LIBRARY_PATH as well as setting PYTHONPATH to a value dependent upon how Elemental was instructed to install the Python interface. In the default case, where Python is installed into the global site packages directory, PYTHONPATH should be set to the result of:

from distutils.sysconfig import get_python_lib
print get_python_lib()


which may have a value suh as $(HOME)/anaconda/lib/python2.7/site-packages. In cases where the CMake option INSTALL_PYTHON_PACKAGE=OFF was specified, PYTHONPATH should be set to $(CMAKE_INSTALL_PREFIX)/python, whereas, if the CMake option INSTALL_PYTHON_INTO_USER_SITE=ON was specified, then PYTHONPATH should be set to the result of:

import site
print site.USER_SITE


which is frequently $(HOME)/.local/lib/python2.7/site-packages. ### Mac OS X¶ It should typically only be necessary to set PYTHONPATH in the same way as on Linux systems (there should be no need to set LD_LIBRARY_PATH, nor its OS X equivalent, DYLD_LIBRARY_PATH). ## Elemental as a CMake subproject¶ Note These instructions are somewhat out of date and so an email to users@libelemental.org might be more appropriate for now in order to help with using Elemental as a subproject of another CMake build system. Adding Elemental as a dependency into a project which uses CMake for its build system can be relatively straightforward: simply put an entire copy of the Elemental source tree in a subdirectory of your main project folder, say external/elemental, and then create a CMakeLists.txt file in your main project folder that builds off of the following snippet: cmake_minimum_required(VERSION 2.8.8) project(Foo) add_subdirectory(external/elemental) include_directories("${PROJECT_BINARY_DIR}/external/El/include")
include_directories(${MPI_CXX_INCLUDE_PATH}) # Build your project here # e.g., # add_library(foo${LIBRARY_TYPE} \${FOO_SRC})

If you run into build problems, please email maint@libelemental.org and make sure to attach the file include/El/config.h, which should be generated within your build directory. Please only direct usage questions to users@libelemental.org, and development questions to dev@libelemental.org.