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# 4 Installation

### Sections

1. Installing Alnuth
2. Getting PARI/GP
3. Adjust the path of the executable for GP
4. Loading and testing the package

This package provides an interface between GAP and PARI/GP. PARI/GP itself is not part of this package. It has to be obtained and installed independently of this package. Alnuth works with PARI/GP Version 2.5 or higher.

## 4.1 Installing Alnuth

The package Alnuth is part of the standard distribution of GAP so that in most cases there is no need to install it separately. To use Alnuth you need to have PARI/GP installed. See the following section for information on PARI/GP.

In case you want to update Alnuth independently of your main GAP installation or if you are interested in an old version of Alnuth interfacing to KANT/KASH you can find all released versions of Alnuth in the form of gzipped tar-archives at https://github.com/gap-packages/alnuth/releases

There are two ways of installing a GAP package. If you have permission to add files to the installation of GAP on your system you may install Alnuth into the `pkg` subdirectory of the GAP installation tree. Otherwise you may install Alnuth in a private `pkg` directory (for details see Subsections Installing a GAP Package and GAP Root Directories in the GAP reference manual).

To install the latest version of Alnuth download one of the archives `alnuth.tar.gz`, move it to the directory `pkg` in which you want to install, and unpack the archive. If you are using the command line you can unpack with the command `tar xzf alnuth.tar.gz`.

## 4.2 Getting PARI/GP

Using Alnuth requires an installation of PARI/GP in Version 2.5 or higher. The software PARI/GP is freely available at https://pari.math.u-bordeaux.fr/

Note that the place where PARI/GP is located in your system is independent of the place where Alnuth is installed.

(a)
  Installing under Linux

  In many Linux distributions PARI/GP can be installed via the software package manager, but this might sometimes be an older version which cannot be used together with Alnuth. (Starting GP from the command line with the option `--version-short` will show you the version number.)

  If you install PARI/GP from source make sure you install with GMP support for better performance and complete the installation with `make install` so that you can start GP by just calling `gp` from the command line.

(b)
  Installing under Windows

  For Windows it is sufficient to get the basic GP binary which can be found at https://pari.math.u-bordeaux.fr/download.html

## 4.3 Adjust the path of the executable for GP

This package needs to know where the executable for GP is. In the default setting Alnuth looks for an executable program named `gp` in the search paths of the system. More precisely, for a file `gp` inside one of the directories in the list returned by `DirectoriesSystemPrograms()` (called in a GAP session).

Under Linux the default setting should work with a standard installation of PARI/GP.

For the default setting to work under Windows the downloaded executable file, for example `gp-2-5-0.exe` has to be renamed to `gp.exe` and moved to one of the directories listed by `DirectoriesSystemPrograms()` (Ignore the leading `cygdrive` in each path name and note that the single letter specifies the drive, for example `/cygdrive/c/Windows/` denotes the folder `Windows` on drive `C:`).

To check whether an executable of GP in Version 2.5 or higher is available with the default setting, you can use the function

- `PariVersion( )`

  which prints the verion number, if the global variable `AL_EXECUTABLE` is bound to the file name of a GP executable.

  If you cannot use the default setting for you purpose, you have two options to specify a new place and name for the GP executable.

  If you are able to edit the file `defs.g` in the main directory of Alnuth, then you can change the line

          BindGlobal("AL_EXECUTABLE", Filename(DirectoriesSystemPrograms(), "gp"));

  to something like

          BindGlobal("AL_EXECUTABLE", "/home/my/pari-2.5.0/gp");

  under Linux or

          BindGlobal("AL_EXECUTABLE", "/cygdrive/c/Users/my/Downloads/gp-2-5-0");

  under Windows, where the second argument gives the path to the GP executable you want to use (Change the strings given above to reflect the actual path on your system.). Please note that in case of a new installation of Alnuth you will have to change `defs.g` again.

  Alternatively you can also change your personal `gaprc` file (see the Subsection The gaprc file in the GAP reference manual) for setting the variable AL_EXECUTABLE to a proper value. To do this add the appropriate line from above with the `BindGlobal` command to `gaprc`.

  The third possibility is to change the path to the GP executable from within GAP using one of the following two functions. To do this you first have to load the package (see Section Loading and testing the package).

- `SetAlnuthExternalExecutable(` path`)`

  adjusts the global variable `AL_EXECUTABLE` for the current GAP session. Depending on your installation of PARI/GP and your operating system the string path has to be either the command to start GP in a terminal (for example `gp`) or the complete path to the executable of GP (for example `/cygwindrive/c/windows/gp`). The function returns `fail` if path does not execute GP in Version 2.5.0 or higher.

  To make the change take effect for all of your GAP sessions, you can add `SetKantExecutable` with the path to the GP executable as argument to your personal `gaprc` file (see the Subsection The gaprc file in the GAP reference manual).

  If you want the change to affect all GAP session of all users of the GAP installation you can use the following function:

- `SetAlnuthExternalExecutablePermanently(` path`)`

  does the same as `SetAlnuthExternalExecutable` and in addition trys to change the file `defs.g` accordingly in the currently loaded version of Alnuth. A warning is issued if there is no write access to `defs.g` from the current GAP session.

- `RestoreAlnuthExternalExecutable( )`

  trys to restore the original content of the file `defs.g` in the directory corresponding to the loaded version of Alnuth. The function returns `fail` if there is no write access to `defs.g` from the current GAP session.

  ## 4.4 Loading and testing the package

  If Alnuth is not loaded when GAP is started you have to request it explicitly to use it. This is done by calling `LoadPackage("Alnuth");` in a GAP session. If Alnuth had not been loaded already a short banner will be displayed.

          gap> LoadingPackage("alnuth");
          Loading  Alnuth 3.2.1 (Algebraic number theory and an interface to PARI/GP)
          by Bjoern Assmann,
             Andreas Distler (a.distler@tu-bs.de), and
             Bettina Eick (http://www.iaa.tu-bs.de/beick).
          maintained by:
             The GAP Team (support@gap-system.org).
          Homepage: https://gap-packages.github.io/alnuth
          Report issues at https://github.com/gap-packages/alnuth/issues
          true
          gap>

  To load a certain version of Alnuth you can specify the version number as second argument in the call to `LoadPackage`. (See `77.2 Loading a GAP package` in the reference manual or type `?LoadPackage` within a GAP session).

  Once the package is loaded, it is possible to check the correct installation running a short test by calling `ReadPackage("Alnuth", "tst/testinstall.tst");`.

          gap> ReadPackage("Alnuth", "tst/testinstall.g");
          Architecture: aarch64-apple-darwin21.4.0-default64-kv8

          testing: GAPROOT/pkg/alnuth/tst/ALNUTH.tst
                66 ms (33 ms GC) and 11.0MB allocated for GAPROOT/pkg/alnuth/tst/ALNUTH.tst
          testing: GAPROOT/pkg/alnuth/tst/version.tst
                21 ms (21 ms GC) and 29.6KB allocated for GAPROOT/pkg/alnuth/tst/version.tst
          -----------------------------------
          total        87 ms (54 ms GC) and 11.0MB allocated
                        0 failures in 2 files

          #I  No errors detected while testing
          gap>

  The architecture, timings and memory usage will usually differ; other discrepancies in the output indicate some problem.

  If the test suite runs into an error in the first part, which verifies the availability of PARI/GP, check your installation of PARI/GP and consult the last chapter of the documentation of Alnuth for more information.

  If you find any bugs or have any suggestions or comments, we would very much appreciate it if you would let us know by submitting an issue at the Alnuth issue tracker on GitHub https://github.com/gap-packages/alnuth/issues

  or by writing an mail to support@gap-system.org.

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