.. _sec-launching:

Launching SageMath
==================

Now we assume that you installed SageMath properly on your system. This
section quickly explains how to start the Sage console and the Jupyter
Notebook from the command line.

If you did install the Windows version or the macOS application you
should have icons available on your desktops or launching menus. Otherwise
you are strongly advised to create shortcuts for Sage as indicated in the part
6 of the "Installation steps" Section in :ref:`build-from-source-step-by-step`.
Assuming that you have this shortcut, running

.. code-block:: console

    $ sage

in a console starts a Sage session.  To quit the session enter ``quit`` and
then press ``<Enter>``.

To start a Jupyter Notebook instead of a Sage console, run the command

.. code-block:: console

    $ sage -n jupyter

instead of just ``sage``. To quit the Jupyter Notebook press ``<Ctrl> + <c>``
twice in the console where you launched the command.

You can pass extra parameters to this command. For example,

.. code-block:: console

    $ sage -n jupyter --port 8899

will run the Jupyter server on a port different from the default (8888).
In particular on WSL, this is very useful because Jupyter may not be able to
detect whether the default port is already taken by another instance of
Jupyter running in Windows.


Environment variables
---------------------

Sage uses the following environment variables when it runs:

- :envvar:`DOT_SAGE` - this is the directory, to which the user has read and
  write access, where Sage stores a number of files.
  The default location is :file:`$HOME/.sage/`.

- :envvar:`SAGE_STARTUP_FILE` - a file including commands to be executed every
  time Sage starts.
  The default value is :file:`$DOT_SAGE/init.sage`.

- :envvar:`BROWSER` - on most platforms, Sage will detect the command to
  run a web browser, but if this doesn't seem to work on your machine, set this
  variable to the appropriate command.

- :envvar:`TMPDIR` - this variable is used by Python, and hence by
  Sage; it gives the directory in which temporary files should be
  stored. This includes files used by the notebook. Some browsers have
  security settings which restrict the locations of files that they
  will access, and users may need to set this variable to handle this
  situation.

- See
  https://docs.python.org/3/using/cmdline.html#environment-variables
  for more variables used by Python (not an exhaustive list).
  A brief summary can also be obtained by running ``python3 --help-env``.

Using a Jupyter Notebook remotely
---------------------------------

If Sage is installed on a remote machine to which you have ``ssh`` access, you
can launch a Jupyter Notebook using a command such as

.. code-block:: console

    $ ssh -L localhost:8888:localhost:8888 -t USER@REMOTE sage -n jupyter --no-browser --port=8888

where ``USER@REMOTE`` needs to be replaced by the login details to the remote
machine. This uses local port forwarding to connect your local machine to the
remote one. The command will print a URL to the console which you can copy and
paste in a web browser.

Note that this assumes that a firewall which might be present between server
and client allows connections on port 8888. See details on port forwarding on
the internet, e.g. https://www.ssh.com/ssh/tunneling/example.

.. _sec-launching-wsl-post-installation:

WSL Post-installation steps
---------------------------

If you've installed SageMath from source on WSL, there are a couple of extra steps you can do to make your life easier:


Create a notebook launch script
"""""""""""""""""""""""""""""""

If you plan to use JupyterLab, install that first.

Now create a script called ``~/sage_nb.sh`` containing the following lines, and fill in the correct paths for your desired starting directory and ``SAGE_ROOT``


.. code-block:: bash

    #!/bin/bash
    # Switch to desired windows directory
    cd /mnt/c/path/to/desired/starting/directory
    # Start the Jupyter notebook
    SAGE_ROOT/sage --notebook
    # Alternatively you can run JupyterLab - delete the line above, and uncomment the line below
    #SAGE_ROOT/sage --notebook jupyterlab

Make it executable:

.. code-block:: console

    $ chmod ug+x ~/sage_nb.sh

Run it to test:

.. code-block:: console

    $ cd ~
    $ ./sage_nb.sh

The Jupyter(Lab) server should start in the terminal window, and you windows browser should open a page showing the Jupyter or JupyterLab starting page, at the directory you specified.

Create a shortcut
"""""""""""""""""

This is a final nicety that lets you start the Jupyter or JupyterLab server in one click:

* Open Windows explorer, and type ``%APPDATA%\Microsoft\Windows\Start Menu\Programs`` in the address bar and press enter. This is the folder that contains you start menu shortcuts. If you want the sage shortcut somewhere else (like your desktop), open that folder instead.
* Open a separate window and go to ``%LOCALAPPDATA%\Microsoft\WindowsApps\``
* Right-click-drag the ``ubuntu.exe`` icon from the second window into the first, then choose ``Create shortcuts here`` from the context menu when you drop it.
* To customize this shortcut, right-click on it and choose properties.

  * On the General tab:

    * Change the name to whatever you want, e.g. "Sage 9.2 JupyterLab"

  * On the Shortcut tab:

    * Change Target to: ``ubuntu.exe run ~/sage_nb.sh``
    * Change Start in to: ``%USERPROFILE%``
    * Change Run to: Minimised
    * Change the icon if you want

Now hit the start button or key and type the name you gave it. it should appear in the list, and should load the server and fire up your browser when you click on it.

------------------------------------------------------------------------

For further reading you can have a look at the other documents in the
SageMath documentation at http://doc.sagemath.org/.


.. _sec-launching-system-jupyter:

Setting up SageMath as a Jupyter kernel in an existing Jupyter notebook or JupyterLab installation
--------------------------------------------------------------------------------------------------

By default, SageMath installs itself as a Jupyter kernel in the same
environment as the SageMath installation. This is the most convenient way to
use SageMath in a Jupyter notebook. To check if the Sage kernel is
available, start a Jupyter notebook and look for the kernel named
``SageMath <x.y.z>`` in the list of available kernels.
Alternatively, you can use the following command to check which kernels are
available:

.. code-block:: console

    $ jupyter kernelspec list
    Available kernels:
      python3     <path to env>/share/jupyter/kernels/python3
      sagemath    <path to env>/share/jupyter/kernels/sagemath

In case the Sage kernel is not listed, you can check if the file ``kernel.json``
is present in ``<path to env>/share/jupyter/kernels/sagemath``.
If it is not there, you can create it using ``jupyter kernelspec install``
as described below.

You may already have a global installation of Jupyter. For added
convenience, it is possible to link your installation of SageMath into
your Jupyter installation, adding it to the list of available kernels
that can be selected in the notebook or JupyterLab interface.

Assuming that SageMath can be invoked by typing ``sage``, you can use

.. code-block:: console

    $ sage -sh -c 'ls -d $SAGE_VENV/share/jupyter/kernels/sagemath'

to find the location of the SageMath kernel description.
Alternatively, use ``jupyter kernelspec list`` from the same environment
where SageMath is installed to find the location of the SageMath kernel.

Now pick a name for the kernel that identifies it clearly and uniquely.

For example, if you install Sage from source tarballs, you could decide
to include the version number in the name, such as ``sagemath-9.6``.
If you build SageMath from a clone of the git repository, it is better to
choose a name that identifies the directory, perhaps ``sagemath-dev``
or ``sagemath-teaching`` because the version will change.

Now assuming that the Jupyter notebook can be started by typing
``jupyter notebook``, the following command will install SageMath as a
new kernel named ``sagemath-dev``.

.. code-block:: console

    $ jupyter kernelspec install --user $(sage -sh -c 'ls -d $SAGE_VENV/share/jupyter/kernels/sagemath') --name sagemath-dev

The ``jupyter kernelspec`` approach by default does lead to about 2Gb of
SageMath documentation being copied into your personal jupyter configuration
directory. You can avoid that by instead putting a symlink in the relevant spot
and

.. code-block:: console

    $ jupyter --paths

to find valid data directories for your Jupyter installation.
A command along the lines of

.. code-block:: console

    $ ln -s $(sage -sh -c 'ls -d $SAGE_VENV/share/jupyter/kernels/sagemath') $HOME/.local/share/jupyter/kernels/sagemath-dev

can then be used to create a symlink to the SageMath kernel description
in a location where your own ``jupyter`` can find it.

If you have installed SageMath from source, the alternative command

.. code-block:: console

    $ ln -s $(sage -sh -c 'ls -d $SAGE_ROOT/venv/share/jupyter/kernels/sagemath') $HOME/.local/share/jupyter/kernels/sagemath-dev

creates a symlink that will stay current even if you switch to a different Python version
later.

To get the full functionality of the SageMath kernel in your global
Jupyter installation, the following Notebook Extension packages also
need to be installed (or linked) in the environment from which the
Jupyter installation runs.

You can check the presence of some of these packages using the command
``jupyter nbextension list``.

 - For the Sage interacts, you will need the package
   ``widgetsnbextension`` installed in the Python environment of the
   Jupyter installation.  If your Jupyter installation is coming from
   the system package manager, it is best to install
   ``widgetsnbextension`` in the same way.  Otherwise, install it
   using ``pip``.

   To verify that interacts work correctly, you can evaluate the following code
   in the notebook::

     @interact
     def _(k=slider(vmin=-1.0, vmax= 3.0, step_size=0.1, default=0), auto_update=True):
     plot([lambda u:u^2-1, lambda u:u+k], (-2,2),
          ymin=-1, ymax=3, fill={1:[0]}, fillalpha=0.5).show()

 - For 3D graphics using Three.js, by default, internet connectivity
   is needed, as SageMath's custom build of the Javascript package
   Three.js is retrieved from a content delivery network.

   To verify that online 3D graphics with Three.js works correctly,
   you can evaluate the following code in the notebook::

     plot3d(lambda u,v:(u^2+v^2)/4-2,(-2,2),(-2,2)).show()

   However, it is possible to configure graphics with Three.js for
   offline use.  In this case, the Three.js installation from the Sage
   distribution needs to be made available in the environment of the
   Jupyter installation.  This can be done by copying or symlinking.
   The Three.js installation in the environment of the Jupyter
   installation must exactly match the version that comes from the
   Sage distribution.  It is not supported to use several Jupyter
   kernels corresponding to different versions of the Sage distribution.

   To verify that offline 3D graphics with Three.js works correctly,
   you can evaluate the following code in the notebook::

     plot3d(lambda u,v:(u^2+v^2)/4-2,(-2,2),(-2,2), online=False).show()

 - For 3D graphics using jsmol, you will need the package
   ``jupyter-jsmol`` installed in the Python environment of the
   Jupyter installation. You can install it using ``pip``.
   (Alternatively, you can copy or symlink it.)

   To verify that jsmol graphics work correctly, you can evaluate the
   following code in the notebook::

     plot3d(lambda u,v:(u^2+v^2)/4-2,(-2,2),(-2,2)).show(viewer="jmol")

Using Jupyter notebook through Visual Studio Code (VS Code) in WSL
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

If you have installed Sage on Windows using Windows Subsystem for
Linux (WSL), it is convenient to use Visual Studio Code (VS Code)
to interact with Sage.

Here are steps to use SageMath in a Jupyter notebook in VS Code:

* Install and run `VS Code <https://code.visualstudio.com/download>`_
  in Windows.

* Click the "Extension" icon on the left (or press :kbd:`Ctrl` +
  :kbd:`Shift` + :kbd:`X`) to open a list of extensions. Install the
  "WSL" and "Jupyter" extensions.

* In the command palette (:kbd:`Ctrl` + :kbd:`Shift` + :kbd:`P`),
  enter "Remote-WSL: New Window", and hit :kbd:`Enter`.

* In the command palette, enter "Create: New Jupyter Notebook", and
  hit :kbd:`Enter`.

* Click "Select Kernel" on the right (or press :kbd:`Ctrl` +
  :kbd:`Alt` + :kbd:`Enter`), select SageMath, and hit :kbd:`Enter`.
