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Back to [[Doc/Heuristic]].

= LP solver support =

Some configurations of the search component of Fast Downward, such as optimal cost partitioning for landmark heuristics, require a linear programming (LP) solver and will complain if the planner has not been built with support for such a solver. Setting up LP support requires three steps, explained below:

 1. Installing one or more LP solvers.
 1. Installing the Open Solver Interface.
 1. Building Fast Downward with LP support.

== Step 1. Installing one or more LP solvers ==

Fast Downward uses a generic interface (see next step) for accessing LP solvers and hence can be used together with different LP solvers. Currently, three LP solvers are supported: CPLEX, Gurobi, and COIN-LP. You can install one, two or all three solvers without causing conflicts. The solver used by the planner is selected by command-line arguments, not at compile time. We recommend using CPLEX, which in our experiments has led to better performance than COIN-LP. We have no experience with Gurobi, but others recommend it over CPLEX. (If you have data comparing these two within Fast Downward, we would be very interested in hearing about it.)

=== Installing one or more LP solvers: CPLEX ===

IBM offers a [[https://developer.ibm.com/academic/|free academic license]] that includes access to CPLEX.
Once you are registered, you can download the 64 bit binary from the member area of the [[https://ibm.onthehub.com|Academic Initiative Website]]. Execute the binary and follow the guided installation. If you want to install in a global location, you have to execute the installer as {{{root}}}.

After the installation, set the following environment variable (adapt the path if you did not install in the default location):
{{{
export DOWNWARD_CPLEX_ROOT64=/opt/ibm/ILOG/CPLEX_Studio1263/cplex
}}}

If you need 32 bit builds, you also have to install the 32 bit version of CPLEX and use the environment variable {{{DOWNWARD_CPLEX_ROOT32}}} to identify its location. However, CPLEX will no longer support 32-bit builds starting with version 12.7 and previous 32-bit versions of CPLEX are not compatible with recent OS versions. If you get segmentation faults with 32-bit CPLEX builds, try to build one of the sample programs that come with CPLEX to see if it is installed correctly.

If you don't want to permanently modify your environment, you can also set these variables directly when calling CMake, or in {{{src/build.py}}}. The variables need to be set for when installing the Open Solver Interface (Step 2.) and when building Fast Downward's search component (Step 3.).

For instructions for Windows, see below.

=== Installing one or more LP solvers: Gurobi ===

We have no experience with installing Gurobi. On Linux, Gurobi is only available for 64bit, which means that it cannot be used with our default (32bit) build.

After the installation, set the following environment variables:
{{{
export DOWNWARD_GUROBI_ROOT=/path/to/gurobi
}}}

If you don't want to permanently modify your environment, you can also set these variables directly when calling CMake, or in {{{src/build.py}}}. The variables need to be set for when installing the Open Solver Interface (Step 2.) and when building Fast Downward's search component (Step 3.).

=== Installing one or more LP solvers: COIN-LP ===

COIN-LP is included in the download for the Open Solver Interface up to and including version 0.103.0. In those version, it is available without additional work after the following step. In other versions it needs to be installed separately. However, we recommend against using it in serious experiments unless you have established that it offers comparable performance to CPLEX in your setting.

== Step 2. Installing the Open Solver Interface ==

The Open Solver Interface (OSI) provides a common interface to different LP solvers. OSI must be compiled '''after''' installing the LP solver(s) in Step 1. If you install a solver later, repeat the installation steps of OSI. We assume in the following that CPLEX and Gurobi are installed and the environment variables {{{DOWNWARD_CPLEX_ROOT}}} and {{{DOWNWARD_GUROBI_ROOT}}} are set up correctly.

These instructions apply to COIN/OSI 0.103.0, which was the last version that was bundled with Fast Downward. Newer versions from http://www.coin-or.org/download/source/Osi/ should work, too. If you experience problems, please [[HomePage#contact|let us know]].

=== Installing the Open Solver Interface on Linux ===

Run the following commands. If you have chosen not to install CPLEX and/or Gurobi, '''omit''' the options related to these solvers from the call to {{{./configure}}} (options for solvers that are not installed can lead to very cryptic error messages). If you install a current version of OSI that does not include CLP and you have installed CLP separately, also add the corresponding options for CLP. This is not necessary for versions that come with a bundled CLP. You may have to include the path to shared libraries in {{{LDFLAGS}}}, i.e. {{{LDFLAGS="-L$DOWNWARD_CPLEX_ROOT/lib -L/usr/lib/gcc/i686-linux-gnu/4.8"}}}. If there are other problems, see the [[#Troubleshooting|troubleshooting section]].


{{{#!highlight bash
set -u
OSI_VERSION=0.103.0
wget http://www.coin-or.org/download/source/Osi/Osi-$OSI_VERSION.tgz
tar xvzf Osi-$OSI_VERSION.tgz
cd Osi-$OSI_VERSION

sudo ./configure CC="gcc" CFLAGS="-m32 -pthread -Wno-long-long" \
                 CXX="g++" CXXFLAGS="-m32 -pthread -Wno-long-long" \
                 LDFLAGS="-L$DOWNWARD_CPLEX_ROOT/lib -L$DOWNWARD_GUROBI_ROOT/lib" \
                 --without-lapack --enable-static=yes \
                 --prefix="path/to/coin" \
                 --with-cplex-incdir=$DOWNWARD_CPLEX_ROOT/include/ilcplex --with-cplex-lib="-lcplex -lm" \
                 --with-gurobi-incdir=$DOWNWARD_GUROBI_ROOT/include_dir --with-gurobi-lib="-lgurobi"
sudo make
sudo make install
cd ..
rm -rf Osi-$OSI_VERSION
rm Osi-$OSI_VERSION.tgz
}}}

After installation, set the environment variable {{{DOWNWARD_COIN_ROOT}}} to the prefix you used in the call to {{{./configure}}}. For example:
{{{
export DOWNWARD_COIN_ROOT=/opt/coin
}}}

If you want to compile for 64-bit, change {{{-m32}}} to {{{-m64}}} in the configuration step above. You also have to change the setting for {{{--prefix}}}, otherwise the 64-bit version will overwrite the 32-bit version. You can then use the environment variables {{{DOWNWARD_COIN_ROOT32}}} and {{{DOWNWARD_COIN_ROOT64}}} to identify the two versions.

If you don't want to permanently modify your environment, you can also set these variables directly when calling CMake, or in {{{src/build.py}}}. The variables need to be set for when installing the Open Solver Interface (Step 2.) and when building Fast Downward's search component (Step 3.).

=== Installing the Open Solver Interface on Mac OS X ===

Follow the Linux instructions above with the following changes:
 * Replace {{{-m32}}} with {{{-arch i386}}}.
 * Building {{{CoinUtils}}} can create both static and dynamic libraries and there have been reported problems with both.
   * To use static libraries, delete the dynamic libraries from {{{$(DOWNWARD_COIN_ROOT)/lib/}}} after building {{{CoinUtils}}}.
   * '''or'''
   * To use dynamic libraries, replace {{{--enable-static=yes}}} with {{{--enable-static=no}}} and change the Fast Downward CMakefile to look for dynamic (*.dylib) instead of static (*.a) libraries of libOsiCpx, libOsiGrb, and libOsiClp.



Installation has been reported to fail on Mac OS X due to a bug in the {{{CoinUtils}}} configure script. (See [[http://issues.fast-downward.org/issue295|issue295]].) If you run into this problem, try downloading the [[attachment:coinutils-configure.patched|patched file]] attached to this page, make it executable, and replace the file {{{Osi-0.103.0/CoinUtils/configure}}} with it:

{{{#! highlight bash
    cp Dowloads/coinutils-configure.patched Osi-0.103.0/CoinUtils/configure
    chmod +x Osi-0.103.0/CoinUtils/configure
}}}

=== Installing the Open Solver Interface on Windows ===

We managed to install OSI with support for CPLEX on Windows using {{{msys2}}} using the following steps:

 1. Install CPLEX into a directory without spaces. We assume this is {{{C:\cplex}}}. Usually you will install ILOG Studio, which contains more than just CPLEX, so the paths below use {{{C:\cplex\cplex}}} to point to the CPLEX part of it.
 1. Install [[http://sourceforge.net/projects/msys2/|msys2]] (this is only necessary to compile Osi and not required to compile the planner)
 1. Within msys2 use pacman to install base-devel: {{{pacman -S base-devel}}}
 1. Download Osi (we use 0.103.0, newer versions should work but are untested) and unpack to {{{C:\msys64\home\<username>\Osi-0.103.0}}}
 1. Start the "VS2013 x86 Native Tools Command Prompt", log in to msys from there, and change to the Osi directory:
    {{{#!highlight bash
    C:\msys64\usr\bin\bash --login -i
    cd Osi-0.103.0
    }}}
 1. Compile debug version of OSI:
    {{{#!highlight bash
    mkdir /c/osi
    mkdir /c/osi/mtd
    LD='link' STRIP=':' AR='lib' RANLIB=':' NM='dumpbin -symbols' \
    CC='cl -nologo' CFLAGS=' -MTd -Zi -FS' CXX='cl -nologo' CXXFLAGS=' -MTd -Zi -EHsc -FS' \
    ./configure --host=x86_64-w64-mingw32 \
                --build=mingw32 \
                --prefix=/c/osi/mtd \
                --with-cplex-lib='-L/c/cplex/cplex/lib/x86_windows_vs2013/stat_mtd/cplex1262.lib' \
                --with-cplex-incdir='/c/cplex/cplex/include/ilcplex' \
                --disable-cplex-libcheck
    make
    make install
    }}}
    Afterwards, copy the debug symbol file {{{C:\msys64\home\<username>\Osi-0.103.0\vc120.pdb}}} to {{{C:\osi\mtd\lib\}}} to avoid compiler warnings when compiling a debug version.
 1. Compile release version of OSI. Note the subtle differences to the command above: we use the directory {{{/c/osi/mt}}} instead of {{{/c/osi/mtd}}} in two places, the flag {{{-MT}}} instead of {{{-MTd}}} in two places, and the CPLEX library {{{stat_mta}}} instead of {{{stat_mtd}}}:

    {{{#!highlight bash
    mkdir /c/osi
    mkdir /c/osi/mt
    LD='link' STRIP=':' AR='lib' RANLIB=':' NM='dumpbin -symbols' \
    CC='cl -nologo' CFLAGS=' -MT -Zi -FS' CXX='cl -nologo' CXXFLAGS=' -MT -Zi -EHsc -FS' \
    ./configure --host=x86_64-w64-mingw32 \
                --build=mingw32 \
                --prefix=/c/osi/mt \
                --with-cplex-lib='-L/c/cplex/cplex/lib/x86_windows_vs2013/stat_mta/cplex1262.lib' \
                --with-cplex-incdir='/c/cplex/cplex/include/ilcplex' \
                --disable-cplex-libcheck
    make
    make install
    }}}

To compile a 64-bit version, start the "VS2013 x64 Native Tools Command Prompt" in step 5 instead of the x86 one. Then chose the 64-bit version of CLPEX in steps 6. and 7., and use a different prefix, e.g., {{{--prefix=/c/osi/mt64}}}. Everything else stays the same (in particular {{{--host=x86_64-w64-mingw32}}} and {{{--build=mingw32}}} do not change).

Note that linking under Windows only works if the libraries were compiled with the same flags. For example, if OSI is compiled with the flag {{{-MTd}}} (dynamic debug) then the planner also has to use this flag for compilation.

In our CMake build system some flags are automatically determined by the build type, e.g., if CMake is called with {{{CMAKE_BUILD_TYPE=DEBUG}}}, the flag {{{-MTd}}} is added by default. The CPLEX library also has to fit to everything. This is important when compiling Osi (in the --with-cplex-lib paramater, see above) and when compiling Fast Downward (handled by the CMake file). CPLEX has precompiled libraries for different versions of Visual Studio each as a static release and static debug version. This is documented in the file {{{C:/cplex/cplex/c_cpp.html}}}.

To allow both debug and release builds of 32- and 64-bit version to link against the correct version of OSI, set the following environment variables:
    {{{#!highlight bash
    DOWNWARD_COIN_ROOT_RELEASE32=C:/osi/mt
    DOWNWARD_COIN_ROOT_DEBUG32=C:/osi/mtd
    DOWNWARD_COIN_ROOT_RELEASE64=C:/osi/mt64
    DOWNWARD_COIN_ROOT_DEBUG64=C:/osi/mtd64
    }}}


== Step 3. Building Fast Downward with LP support ==

Once OSI is installed, you can build Fast Downward's search component with LP support by calling {{{./build.py}}}. Remove your previous build first:
{{{
rm -rf builds
}}}

Fast Downward automatically includes an LP Solver in the build, if it is needed, and the solver and the necessary OSI adapter are detected on the system. If you want to explicitly build without the LP solver that is installed on your system, disable the LP solver plugin (with {{{-DPLUGIN_LP_SOLVER_ENABLED=FALSE}}}) and all plug-ins that require it, such as {{{POTENTIAL_HEURISTICS}}} (see ObtainingAndRunningFastDownward#Manual_Builds).

== Troubleshooting ==

The LP-related libraries have a number of dependencies which might not be installed on your system. If for some reason one of the above steps fails, we would appreciate if you could attempt to troubleshoot it yourself.

If the configure step of COIN/OSI fails with the error {{{Cannot find symbol(s) CPXgetstat with CPX}}}, check the path to the CPLEX lib directory. Depending on your CPLEX installation, the libraries might be stored in a different place, e.g., in {{{$DOWNWARD_CPLEX_ROOT/lib/x86_linux/static_pic}}}. Check that the directory exists and contains the file {{{libcplex.a}}}. If the configure step fails for another reason, have a look at their [[https://projects.coin-or.org/BuildTools/wiki/user-troubleshooting|troubleshooting page]] or their page of [[https://projects.coin-or.org/BuildTools/wiki/current-issues|current issues]].

If you get warnings about unresolved references with CPLEX, visit their [[http://www-01.ibm.com/support/docview.wss?uid=swg21399926|help pages]].

If Fast Downward gives you compilation errors mentioning the `isnan` function, you are likely affected by an OSI/compiler incompatibility (see [[http://issues.fast-downward.org/issue681]]). In this case try the following:

  1. Add `export DOWNWARD_USE_ISNAN_WORKAROUND=1` to your `~/.bashrc` file (or other shell configuration file).
  1. Make sure the changed shell configuration takes effect by logging out and then logging in again.
  1. In the main directory of the repository, delete all cmake build artifacts with `rm -r builds`.
  1. Rebuild.

If installing a 32-bit version of OSI on maia leads to an error about the wrong file format of {{{libstdc++.so}}}, then removing 64-bit specific paths from {{{LD_LIBRARY_PATH}}} might help. For example with g++-4.9.2 on maia, removing {{{/scicore/soft/apps/GCC/4.9.2/lib64}}} helps.

If after troubleshooting you can get the LP package to work, please do let us know of your problem and its solution so that we can improve these instructions. If you still cannot get it to work, we may be able to provide some help, but note that the LP solvers and OSI library are external packages not developed by us.