<?xml version="1.0"?>
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN"
               "http://www.oasis-open.org/docbook/xml/4.3/docbookx.dtd" [
<!ENTITY igraph "igraph">
]>

<chapter id="igraph-Installation">
<title>Installation</title>

<para>
  This chapter describes building igraph from source code and installing it.
  The source archive of the latest stable release is always available
  <ulink url="https://igraph.org/c/#downloads">from the igraph website</ulink>.
  igraph is also included in many Linux distributions, as well as several package
  managers such as <ulink url="https://vcpkg.io/">vcpkg</ulink> (convenient on Windows),
  <ulink url="https://www.macports.org/">MacPorts</ulink> (macOS) and
  <ulink url="https://brew.sh/">Homebrew</ulink> (macOS), which provide an easier
  means of installation. If you decide to use them, please consult their documentation
  on how to install packages.
</para>

<section id="igraph-Installation-prerequisites">
  <title>Prerequisites</title>
  <para>
    To build igraph from sources, you will need at least:
  </para>
  <itemizedlist>
    <listitem>
      <para>
        <ulink url="https://cmake.org">CMake</ulink> 3.18 or later
      </para>
    </listitem>
    <listitem>
      <para>
        C and C++ compilers
      </para>
    </listitem>
  </itemizedlist>
  <para>
    Visual Studio 2015 and later are supported. Earlier Visual Studio
    versions may or may not work.
  </para>
  <para>
    Certain features also require the following libraries:
  </para>
  <itemizedlist>
    <listitem>
      <para>
        <ulink url="http://www.xmlsoft.org/">libxml2</ulink>,
        required for GraphML support
      </para>
    </listitem>
  </itemizedlist>
  <para>
    igraph bundles a number of libraries for convenience. However, it is
    preferable to use external versions of these libraries, which may
    improve performance. These are:
  </para>
  <itemizedlist>
    <listitem>
      <para>
        <ulink url="https://gmplib.org/">GMP</ulink> (the bundled
        alternative is Mini-GMP)
      </para>
    </listitem>
    <listitem>
      <para>
        <ulink url="https://www.gnu.org/software/glpk/">GLPK</ulink> (version 4.57 or later)
      </para>
    </listitem>
    <listitem>
      <para>
        <ulink url="https://www.caam.rice.edu/software/ARPACK/">ARPACK</ulink>
      </para>
    </listitem>
    <listitem>
      <para>
        A library providing a
        <ulink url="https://www.netlib.org/blas/">BLAS</ulink> API
        (available by default on macOS;
        <ulink url="https://www.openblas.net">OpenBLAS</ulink> is one
        option on other systems)
      </para>
    </listitem>
    <listitem>
      <para>
        A library providing a
        <ulink url="https://www.netlib.org/lapack/">LAPACK</ulink>
        API (available by default on macOS;
        <ulink url="https://openblas.net">OpenBLAS</ulink> is one
        option on other systems)
      </para>
    </listitem>
  </itemizedlist>
  <para>
    When building the development version of igraph,
    <literal>bison</literal>, <literal>flex</literal> and
    <literal>git</literal> are also required. Released versions do not
    require these tools.
  </para>
  <para>
    To run the tests, <literal>diff</literal> is also required.
  </para>
</section>

<section id="igraph-Installation-installation">
  <title>Installation</title>
  <section id="igraph-Installation-general-build-instructions">
    <title>General build instructions</title>
    <para>
      igraph uses a
      <ulink url="https://cmake.org/cmake/help/latest/guide/user-interaction/index.html">CMake-based
      build system</ulink>. To compile it,
    </para>
    <itemizedlist>
      <listitem>
        <para>
          Enter the directory where the igraph sources are:
<programlisting>
$ cd igraph
</programlisting>
        </para>
      </listitem>
      <listitem>
        <para>
          Create a new directory. This is where igraph will be built:
<programlisting>
$ mkdir build
$ cd build
</programlisting>
        </para>
      </listitem>
      <listitem>
        <para>
          Run CMake, which will automatically configure igraph, and
          report the configuration:
<programlisting>
$ cmake ..
</programlisting>
          To set a non-default installation location, such as
          <literal>/opt/local</literal>, use:
          <programlisting>cmake .. -DCMAKE_INSTALL_PREFIX=/opt/local</programlisting>
        </para>
      </listitem>
      <listitem>
        <para>
          Check the output carefully, and ensure that all features you
          need are enabled. If CMake could not find certain libraries,
          some features such as GraphML support may have been
          automatically disabled.
        </para>
      </listitem>
      <listitem>
        <para>
          There are several ways to adjust the configuration:
        </para>
        <itemizedlist>
          <listitem>
            <para>
              Run <literal>ccmake .</literal> on Unix-like systems or
              <literal>cmake-gui</literal> on Windows for a convenient
              interface.
            </para>
          </listitem>
          <listitem>
            <para>
              Simply edit the <literal>CMakeCache.txt</literal> file.
              Some of the relevant options are listed below.
            </para>
          </listitem>
        </itemizedlist>
      </listitem>
      <listitem>
        <para>
          Once the configuration has been adjusted, run
          <literal>cmake ..</literal> again.
        </para>
      </listitem>
      <listitem>
        <para>
          Once igraph has been successfully configured, it can be built,
          tested and installed using:
<programlisting>
$ cmake --build .
$ cmake --build . --target check
$ cmake --install .
</programlisting>
        </para>
      </listitem>
    </itemizedlist>
  </section>

  <section id="igraph-Installation-specific-instructions-for-windows">
    <title>Specific instructions for Windows</title>
    <section id="igraph-Installation-microsoft-visual-studio">
      <title>Microsoft Visual Studio</title>
      <para>
        With Visual Studio, the steps to build igraph are generally the
        same as above. However, since the Visual Studio CMake generator is
        a multi-configuration one, we must specify the configuration
        (typically Release or Debug) with each build command using the
        <literal>--config</literal> option:
      </para>
<programlisting>
mkdir build
cd build
cmake ..
cmake --build . --config Release
cmake --build . --target check --config Release
</programlisting>
      <para>
        When building the development version, <literal>bison</literal>
        and <literal>flex</literal> must be available on the system.
        <ulink url="https://github.com/lexxmark/winflexbison"><literal>winflexbison</literal></ulink>
        for Bison version 3.x can be useful for this purpose—make sure
        that the executables are in the system <literal>PATH</literal>.
        The easiest installation option is probably by installing
        <literal>winflexbison3</literal> from the
        <ulink url="https://chocolatey.org/packages/winflexbison3">Chocolatey
        package manager</ulink>.
      </para>
      <section id="igraph-Installation-vcpkg">
        <title>vcpkg</title>
        <para>
          Most external dependencies can be conveniently installed using
          <ulink url="https://github.com/microsoft/vcpkg#quick-start-windows"><literal>vcpkg</literal></ulink>.
          Note that <literal>igraph</literal> bundles all dependencies
          except <literal>libxml2</literal>, which is needed for GraphML
          support.
        </para>
        <para>
          In order to use vcpkg integrate it in the build environment by executing
          <literal>vcpkg.exe integrate install</literal> on the command line.
          When configuring igraph, point CMake to the correct
          <literal>vcpkg.cmake</literal> file using <literal>-DCMAKE_TOOLCHAIN_FILE=...</literal>,
          as instructed.
        </para>
        <para>
          Additionally, it might be that you need to set the appropriate
          so-called triplet using
          <literal>-DVCPKG_TARGET_TRIPLET</literal> when running
          <literal>cmake</literal>, for exampling, setting it to
          <literal>x64-windows</literal> when using shared builds of packages or
          <literal>x64-windows-static</literal> when using static builds.
          Similarly, you also need to specify this target triplet when
          installing packages. For example, to install
          <literal>libxml2</literal> as a shared library, use
          <literal>vcpkg.exe install libxml2:x64-windows</literal> and to
          install <literal>libxml2</literal> as a static library, use
          <literal>vcpkg.exe install libxml2:x64-windows-static</literal>.
          In addition, there is the possibility to use a static library
          with dynamic runtime linking using the
          <literal>x64-windows-static-md</literal> triplet.
        </para>
      </section>
    </section>
      <section id="igraph-Installation-msys2">
      <title>MSYS2</title>
      <para>
        MSYS2 can be installed from <ulink url="https://www.msys2.org/">msys2.org</ulink>. After installing MSYS2,
        ensure that it is up to date by opening a terminal and running
        <literal>pacman -Syuu</literal>.
      </para>
      <para>
        The instructions below assume that you want to compile for a 64-bit
        target.
      </para>
      <para>
        Install the following packages using <literal>pacman -S</literal>.
      </para>
      <itemizedlist>
        <listitem>
          <para>
            Minimal requirements:
            <literal>mingw-w64-x86_64-toolchain</literal>,
            <literal>mingw-w64-x86_64-cmake</literal>.
          </para>
        </listitem>
        <listitem>
          <para>
            Optional dependencies that enable certain features:
            <literal>mingw-w64-x86_64-gmp</literal>,
            <literal>mingw-w64-x86_64-libxml2</literal>
          </para>
        </listitem>
        <listitem>
          <para>
            Optional external libraries for better performance:
            <literal>mingw-w64-x86_64-openblas</literal>,
            <literal>mingw-w64-x86_64-arpack</literal>,
            <literal>mingw-w64-x86_64-glpk</literal>
          </para>
        </listitem>
        <listitem>
          <para>
            Only needed for running the tests: <literal>diffutils</literal>
          </para>
        </listitem>
        <listitem>
          <para>
            Required only when building the development version:
            <literal>git</literal>, <literal>bison</literal>,
            <literal>flex</literal>
          </para>
        </listitem>
      </itemizedlist>
      <para>
        The following command will install of these at once:
      </para>
<programlisting>
pacman -S \
  mingw-w64-x86_64-toolchain mingw-w64-x86_64-cmake \
  mingw-w64-x86_64-gmp mingw-w64-x86_64-libxml2 \
  mingw-w64-x86_64-openblas mingw-w64-x86_64-arpack \
  mingw-w64-x86_64-glpk diffutils git bison flex
</programlisting>
      <para>
        In order to build igraph, follow the <emphasis role="strong">General
        build instructions</emphasis> above, paying attention to the
        following:
      </para>
      <itemizedlist>
        <listitem>
          <para>
            When using MSYS2, start the <quote>MSYS2 MinGW 64-bit</quote>
            terminal, and <emphasis>not</emphasis> the <quote>MSYS2
            MSYS</quote> one.
          </para>
        </listitem>
        <listitem>
          <para>
            Be sure to install the <literal>mingw-w64-x86_64-cmake</literal>
            package and not the <literal>cmake</literal> one. The latter
            will not work.
          </para>
        </listitem>
        <listitem>
          <para>
            When running <literal>cmake</literal>, pass the option
            <literal>-G&quot;MSYS Makefiles&quot;</literal>.
          </para>
        </listitem>
        <listitem>
          <para>
            Note that <literal>ccmake</literal> is not currently available.
            <literal>cmake-gui</literal> can be used only if the
            <literal>mingw-w64-x86_64-qt5</literal> package is installed.
          </para>
        </listitem>
      </itemizedlist>
    </section>
  </section>

  <section id="igraph-Installation-notable-configuration-options">
    <title>Notable configuration options</title>
    <para>
      The following options may be set to <literal>ON</literal> or
      <literal>OFF</literal>. Some of them have an <literal>AUTO</literal>
      setting, which chooses a reasonable default based on what libraries
      are available on the current system.
    </para>
    <itemizedlist>
      <listitem>
        <para>
          igraph bundles some of its dependencies for convenience. The
          <literal>IGRAPH_USE_INTERNAL_XXX</literal> flags control whether
          these should be used instead of external versions. Set them to
          <literal>ON</literal> to use the bundled
          (<quote>vendored</quote>) versions. Generally, external versions
          are preferable as they may be newer and usually provide better
          performance.
        </para>
      </listitem>
      <listitem>
        <para>
          <literal>IGRAPH_GLPK_SUPPORT</literal>: whether to make use of
          the
          <ulink url="https://www.gnu.org/software/glpk/">GLPK</ulink>
          library. Some features, such as finding a minimum feedback arc
          set or finding communities through exact modularity
          optimization, require this.
        </para>
      </listitem>
      <listitem>
        <para>
          <literal>IGRAPH_GRAPHML_SUPPORT</literal>: whether to enable
          support for reading and writing
          <ulink url="http://graphml.graphdrawing.org/">GraphML</ulink>
          files. Requires the
          <ulink url="http://xmlsoft.org/">libxml2</ulink> library.
        </para>
      </listitem>
      <listitem>
        <para>
          <literal>IGRAPH_OPENMP_SUPPORT</literal>: whether to use OpenMP
          parallelization to accelerate certain functions such as PageRank
          calculation. Compiler support is required.
        </para>
      </listitem>
      <listitem>
        <para>
          <literal>IGRAPH_ENABLE_LTO</literal>: whether to build igraph
          with link-time optimization, which improves performance. Not
          supported with all compilers.
        </para>
      </listitem>
      <listitem>
        <para>
          <literal>IGRAPH_ENABLE_TLS</literal>: whether to enable
          thread-local storage. Required when using igraph from multiple
          threads.
        </para>
      </listitem>
      <listitem>
        <para>
          <literal>IGRAPH_WARNINGS_AS_ERRORS</literal>: whether to treat
          compiler warnings as errors. We strive to eliminate all compiler
          warnings during development so this switch is turned on by default.
          If your compiler prints warnings for some parts of the code that we
          did not anticipate, you can turn off this option to prevent the
          warnings from stopping the compilation.
        </para>
      </listitem>
      <listitem>
        <para>
          <ulink url="https://cmake.org/cmake/help/latest/variable/BUILD_SHARED_LIBS.html"><literal>BUILD_SHARED_LIBS</literal></ulink>:
          whether to build a shared library instead of a static one.
        </para>
      </listitem>
      <listitem>
        <para>
          <literal>BLA_VENDOR</literal>: controls which library to use for
          <ulink url="https://cmake.org/cmake/help/latest/module/FindBLAS.html">BLAS</ulink>
          and
          <ulink url="https://cmake.org/cmake/help/latest/module/FindLAPACK.html">LAPACK</ulink>
          functionality.
        </para>
      </listitem>
      <listitem>
        <para>
          <ulink url="https://cmake.org/cmake/help/latest/variable/CMAKE_INSTALL_PREFIX.html"><literal>CMAKE_INSTALL_PREFIX</literal></ulink>:
          the location where igraph will be installed.
        </para>
      </listitem>
    </itemizedlist>
  </section>
</section>

<section id="igraph-Installation-building-the-documentation">
  <title>Building the documentation</title>
  <para>
    Most users will not need to build the documentation, as the release
    tarball contains pre-built HTML documentation in the <literal>doc</literal>
    directory.
  </para>
  <para>
    To build the documentation for the development version, simply build
    the <literal>html</literal> or <literal>pdf</literal> targets for the
    HTML and PDF versions of the documentation, respectively.
  </para>
<programlisting>
$ cmake --build . --target html
</programlisting>
  <para>
    Building the HTML documentation requires Python 3, <literal>xmlto</literal>
    and <literal>source-highlight</literal>. Building the PDF documentation
    also requires <literal>xsltproc</literal>, <literal>xmllint</literal>
    and <literal>fop</literal>.
  </para>
</section>

<section id="igraph-Installation-notes-for-package-maintainers">
  <title>Notes for package maintainers</title>
  <para>
    This section is for people who package igraph for Linux distros or
    other package managers. Please read it carefully before packaging
    igraph.
  </para>
  <section id="igraph-Installation-auto-detection-of-dependencies">
    <title>Auto-detection of dependencies</title>
    <para>
      igraph bundles several of its dependencies (or simplified versions
      of its dependencies). During configuration time, it checks whether
      each dependency is present on the system. If yes, it uses it.
      Otherwise, it falls back to the bundled (<quote>vendored</quote>)
      version. In order to make configuration as deterministic as
      possible, you may want to disable this auto-detection. To do so, set
      each of the <literal>IGRAPH_USE_INTERNAL_XXX</literal> option
      described above. Additionally, set <literal>BLA_VENDOR</literal> to
      use the BLAS and LAPACK implementations of your choice. This should
      be the same BLAS and LAPACK library that igraph's other dependencies
      (e.g., ARPACK) are linked against.
    </para>
    <para>
      For example, to force igraph to use external versions of all
      dependencies, and to use OpenBLAS for BLAS/LAPACK, use
    </para>
    <para>
<programlisting>
$ cmake .. \
    -DIGRAPH_USE_INTERNAL_BLAS=OFF \
    -DIGRAPH_USE_INTERNAL_LAPACK=OFF \
    -DIGRAPH_USE_INTERNAL_ARPACK=OFF \
    -DIGRAPH_USE_INTERNAL_GLPK=OFF \
    -DIGRAPH_USE_INTERNAL_GMP=OFF \
    -DBLA_VENDOR=OpenBLAS \
    -DIGRAPH_GRAPHML_SUPPORT=ON
</programlisting>
    </para>
  </section>
  <section id="igraph-Installation-shared-and-static-builds">
    <title>Shared and static builds</title>
    <para>
      On Windows, shared and static builds should not be installed in the same
      location. If you decide to do so anyway, keep in mind the following:
      Both builds contain an <literal>igraph.lib</literal> file. The static one
      should be renamed to avoid conflict. The headers from the static build
      are incompatible with the shared library. The headers from the shared build
      may be used with the static library, but <literal>IGRAPH_STATIC</literal>
      must be defined when compiling programs that will link to igraph statically.
    </para>
    <para>
      These issues do not affect Unix-like systems.
    </para>
  </section>
  <section id="igraph-Installation-cross-compiling">
    <title>Cross-compiling</title>
    <para>
      When building igraph with an internal ARPACK, LAPACK or BLAS, it
      makes use of f2c, which compiles and runs the <literal>arithchk</literal>
      program at build time to detect the floating point characteristics of the
      current system. It writes the results into the <literal>arith.h</literal>
      header. However, running this program is not possible when cross-compiling
      without providing a userspace emulator that can run executables of the
      target platform on the host system. Therefore, when cross-compiling, you
      either need to provide such an emulator with the
      <literal>CMAKE_CROSSCOMPILING_EMULATOR</literal> option, or you need to
      specify a pre-generated version of the <literal>arith.h</literal> header
      file through the <literal>F2C_EXTERNAL_ARITH_HEADER</literal>
      CMake option. An example version of this header follows for the
      x86_64 and arm64 target architecures on macOS. Warning: Do not use this
      version of <literal>arith.h</literal> on other systems or architectures.
    </para>
    <para>
<programlisting>
#define IEEE_8087
#define Arith_Kind_ASL 1
#define Long int
#define Intcast (int)(long)
#define Double_Align
#define X64_bit_pointers
#define NANCHECK
#define QNaN0 0x0
#define QNaN1 0x7ff80000
</programlisting>
    </para>
    <para>
      igraph also checks whether the endianness of <literal>uint64_t</literal>
      matches the endianness of <literal>double</literal> on the platform
      being compiled. This is needed to ensure that certain functions in igraph's
      random number generator work properly. However, it is not possible to
      execute this check when cross-compiling without an emulator, so in this
      case igraph simply assumes that the endianness matches (which is the case
      for the vast majority of platforms anyway). The only case where you might
      run into problems is when you cross-compile for Apple Silicon
      (<literal>arm64</literal>) from an Intel-based Mac, in which case CMake
      might not realize that you are cross-compiling and will try to execute
      the check anyway. You can work around this by setting
      <literal>IEEE754_DOUBLE_ENDIANNESS_MATCHES</literal> to <literal>ON</literal>
      explicitly before invoking CMake.
    </para>
    <para>
      Providing an emulator in <literal>CMAKE_CROSSCOMPILING_EMULATOR</literal>
      has the added benefit that you can run the compiled unit tests on the
      host platform. We have experimented with cross-compiling to 64-bit ARM
      CPUs (<literal>aarch64</literal>) on 64-bit Intel CPUs (<literal>amd64</literal>),
      and we can confirm that using <literal>qemu-aarch64</literal> works as a
      cross-compiling emulator in this setup.
    </para>
  </section>
  <section id="igraph-Installation-additional-notes">
    <title>Additional notes</title>
    <itemizedlist>
      <listitem>
        <para>
          As of igraph 0.10, there is no tangible benefit to using an
          external GMP, as igraph does not yet use GMP in any
          performance-critical way. The bundled Mini-GMP is sufficient.
        </para>
      </listitem>
      <listitem>
        <para>
          Link-time optimization noticeably improves the performance of
          some igraph functions. To enable it, use
          <literal>-DIGRAPH_ENABLE_LTO=ON</literal>.
          The <literal>AUTO</literal> setting is also supported, and will
          enable link-time optimization only if the current compiler
          supports it. Note that this is detected by CMake, and the
          detection is not always accurate.
        </para>
      </listitem>
      <listitem>
        <para>
          We saw occasional hangs on Windows when igraph was built for a
          32-bit target with MinGW and linked to OpenBLAS. We believe this
          to be an issue with OpenBLAS, not igraph. On this platform, you
          may want to opt for a different BLAS/LAPACK or the bundled
          BLAS/LAPACK.
        </para>
      </listitem>
    </itemizedlist>
  </section>
</section>

</chapter>