# Anaconda

Anaconda is a software manager that allows you download and execute
packages in your home directory.

If you use the Nevis Linux cluster, then you should consider using
{ref}`environment modules <setting-up-root>` over Anaconda. But if
you're on a different system, or the Nevis environment modules don't
offer the package or version you're looking for, Anaconda is a better
choice. You can install Anaconda in your home directory so admin access
is not necessary. Simply follow the [web site
directions](https://docs.conda.io/projects/continuumio-conda/en/latest/user-guide/install/index.html)
to install Miniconda[^f105].

Once you've installed Anaconda, you'll want to include
[conda-forge](https://conda-forge.org/) for packages such as ROOT. The
following commands set it up:

    conda config --add channels conda-forge
    conda config --set channel_priority strict

At this point, you'll probably have log off then log in to your computer
again to give conda a chance to set up your shell.

To install Jupyter/ROOT, with sufficient features for most of this
tutorial:

    conda create --name jupyter-pyroot compilers python jupyter jupyterlab root

Note that the name `jupyter-pyroot` is arbitrary; you can use any name
for the [conda
environment](https://conda.io/projects/conda/en/latest/user-guide/tasks/manage-environments.html)
that you wish.

If you continue to work with Jupyter or ROOT after this tutorial, there are
standard packages that you'll probably want to include:

    conda install --name jupyter-pyroot numpy scipy matplotlib

Your working group may use additional packages. For example, the VERITAS
group at Nevis might want to use (in addition to the above):

    conda install --name jupyter-pyroot astropy gammapy

You only have to go through the above steps once to define an
environment (e.g., `jupyter-pyroot`). Afterwards, once per login
session, it's necessary to activate it:

    conda activate jupyter-pyroot

Once activated, you should be able to run ROOT by simply typing:

    root

You can run jupyterlab with:

    jupyter lab

:::{admonition} Windows users
The above instructions for installing ROOT won't work under
MS-Windows. You can install conda, but the ROOT windowing system so
heavily depends on X11 that ROOT is simply not available in the
conda libraries for Windows.

The solution is to install [Windows Subsystem for
Linux](https://learn.microsoft.com/en-us/windows/wsl/install) (WSL) on
your laptop; you'll probably want to install the
[Ubuntu](https://ubuntu.com/wsl) distribution. Then install conda
within Ubuntu, and continue as above. 

You may also need [MobaXterm](https://mobaxterm.mobatek.net/) to provide ROOT with an
X11 server. 
:::

:::{warning}

-   Conda takes a long time to run. Be patient. I've seen
    some conda environments take hours to install.

-   A conda environment can take up a lot of disk space, since it not
    only installs the packages you list, but any other packages that
    they depend on. On my desktop computer, the minimal Jupyter/ROOT
    container described above takes up 3G. This may not seem like much,
    but summer students at Nevis have a disk quota of 10G.

    It's possible to run into disk-space problems, especially if you're
    sharing disk space with other users, if you add more packages to your
    environment, or you define multiple environments for different
    projects.

-   Anaconda changes your shell's execution environment. It may be
    incompatible with other environment setups (such as MicroBooNE's
    LArSoft, ATLAS' Athena, or Nevis' `module load` command).

-   Your shell's prompt will be changed by conda. Even when you're not
    using conda, the text `(base)` will appear at the beginning of the
    prompt. If this doesn't bother you, then ignore it. If it does, you
    can try:

        conda config --set auto_activate_base false

    You'll have to log off then log in again to see the change. If you
    don't want conda to alter your prompt even when you're using an
    environment, this command will suppress conda's prompt changes:

        conda config --set changeps1 False
:::

:::::{tip}
One of the most common questions I'm asked is how to relocate a conda
environment to some other location than one's home directory:

   - As noted above, conda environments take up a lot of disk
     space. Most research groups have additional disk storage that's
     not part of a home directory; you can read about how the Nevis
     particle-physics groups handle their storage in {ref}`shared
     filesystems`.

   - Many research groups want to share their conda environments, to
     make sure that everyone is using the same versions.

For tips on managing disk space for your conda environments, see
the [Nevis conda wiki
page](https://twiki.nevis.columbia.edu/twiki/bin/view/Main/Conda).
The [conda page on managing environments](https://docs.conda.io/projects/conda/en/latest/user-guide/tasks/manage-environments.html) is also helpful.
:::::

[^f105]: For this tutorial, the full Anaconda set of packages is not
    necessary. Note that all the Nevis particle-physics systems already
    have conda installed.