<h4>6.1 <span class="Heading">Making the HeLP-package run</span></h4>
<p>For all basic functionalities of the HeLP-package (using only the solver normaliz) the standard GAP-installation should suffice to make everything work: Get the most recent GAP from the <span class="URL"><a href="https://www.gap-system.org/">GAP-webpage</a></span> by following the instructions on the Download-page. Make sure to also install all packages needed to run HeLP. Then just start GAP and type <code class="keyw">LoadPackage("HeLP");</code>.</p>
<p>Here is a checklist what to do, if the package does not work or you also want to use the solver 4ti2:</p>
<ul>
<li><p>Make sure you have sufficiently new versions of the following software:</p>
</li>
<li><p>the GAP-package <span class="URL"><a href="https://gap-packages.github.io/io/">IO</a></span> (at least 4.2; see also the next bullet point if this package can not be loaded)</p>
</li>
</ul>
</li>
</ul>
<p>Usually all these packages should come with a sufficiently recent GAP-installation (4.8.3 or newer) and should be contained in the pkg-folder of the GAP-installation. To see if they are working you can load them by typing <code class="keyw">LoadPackage("[name]");</code> after starting GAP, where <code class="keyw">[name]</code> is the name of the package.</p>
<ul>
<li><p>The IO-package needs a C-part to be compiled. To see if this has already been done on your system, you can enter <code class="keyw">LoadPackage("IO");</code> after starting GAP. If the result is <code class="keyw">fail</code> and the package is contained in the pkg-folder, than most likely the C-part is not yet compiled. For information on installation and in particular on how to compile the C-part, see the <span class="URL"><a href="https://gap-packages.github.io/io/doc/chap0.html">manual</a></span> (in particular Chapter 2) or the README-file of that package.</p>
</li>
<li><p>The installation of normaliz is possible via the GAP-package <span class="URL"><a href="https://gap-packages.github.io/NormalizInterface//">NormalizInterface</a></span> (at least 0.9.6). Just access the folder in a terminal and do <code class="keyw">./build-normaliz.sh; ./configure; make</code>.</p>
</li>
<li><p>If you want to use 4ti2, please make sure that <span class="URL"><a href="https://4ti2.github.io">4ti2.github.io</a></span> (Version 1.6.5 or newer) is properly installed. In case of an error-message "The executable 'zsolve' provided by the software 4ti2 was not found." after typing <code class="keyw">LoadPackage("HeLP");</code> either the software is not properly installed or installed in a directory where GAP can not find it, i.e. a directory not contained in the path-variable. The content of this variable can typically be displayed by typing <code class="keyw">echo $PATH</code> (Linux, Mac) <code class="keyw">echo %PATH%</code> (Windows) in a terminal or a command prompt. The manual of 4ti2 contains several pages of information on how to install the program. Note that the installation of 4ti2 requires gcc (g++) and gmp installed (which come with many Linux installations or can be installed using a package manager). Make sure to execute all four commands indicated in the 4ti2 manual (possibly without the <code class="keyw">--prefix=</code>-part):</p>
<p>Depending on the settings of your system you might need root privileges (type <code class="keyw">sudo</code> in front of every command) to unpack the files and install them. To check whether the installation worked, you can enter <code class="keyw">zsolve</code> in a terminal. In case one of the required programs (g++ or gmp) was not installed when running <code class="keyw">make</code> for the first time, you might need to run <code class="keyw">make clean</code> and the above commands afterwards again (several times) to compile 4ti2 successfully. If you already have 4ti2 installed in a directory not contained in the path-variable and want to avoid a re-installation, in many cases the following helps:</p>
<ul>
<li><p>Start a terminal and access a path written in your bash or system_bash. Typically <code class="keyw">usr/local/bin</code> should work.</p>
</li>
<li><p>Run <code class="keyw">ln -s /[PathToZsolve] zsolve</code>, where <code class="keyw">[PathToZsolve]</code> is the path to the executable zsolve. This sets a symlink to the right place. E.g. <code class="keyw">ln -s /opt/4ti2/bin/zsolve zsolve</code> was used on the (Linux) computers in Stuttgart.</p>
</li>
</ul>
</li>
<li><p>In case you use 4ti2, we also recommend to install <span class="URL"><a href="https://cgm.cs.mcgill.ca/~avis/C/lrs.html">lrslib</a></span>, at least version 4.3. This software provides the 'redund'command, which can be switched on and off within HeLP, but which often leads to better performances (cf. <code class="func">HeLP_UseRedund</code> (<a href="chap3_mj.html#X7A7536D9790C1901"><span class="RefLink">3.5-2</span></a>)). For installation see the User's Guide or the Readme-file on the above mentioned homepage. Usually, after unpacking in a directory contained in the path-variable it should be enough to call
<p><code class="keyw">make all</code></p>
<p>(possibly as root) inside the lrslib-directory.</p>
</li>
<li><p>If this does not help to get HeLP running, please feel more than welcome to contact one of the maintainers of the package.</p>
<h4>6.2 <span class="Heading">How much 4ti2 and normaliz is really there?</span></h4>
<p>The reason, why the programs 4ti2 and normaliz are used in this package, is basically that they can solve systems of linear inequalities efficiently and there exist good GAP-Interfaces for them. However there is only one line of code where a function is called which accesses 4ti2 and a few more for normaliz. Thus the effort of using another solver of inequalities would be not so big, if there is a GAP-Interface for it. If you are aware of such a solver and would like to use it in this package, please contact the authors of this package. We will be happy to help.</p>
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