69 Getting started with Julia

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Julia is a freely available, open-source programming language aimed at technical computing.

As it is open source, indeed with a liberal MIT license, it can be installed for free on many types of computers (though not phones or tablets).

69.1 Running Julia through the web

There are a few services for running Julia through the web. Mentioned here is Binder, which provides a web-based interface to Julia built around Jupyter. Jupyter is a wildly successful platform for interacting with different open-source software programs.

launch binder

Clicking the launch link above will open a web page which provides a blank notebook, save for a package used by these notes. However, Binder is nowhere near as reliable as a local installation.

69.2 Installing Julia locally

Installing Julia locally is not more difficult than installing other software.

Binaries of Julia are provided at julialang.org. Julia has an official released version and a developmental version. Unless there is a compelling reason, the latest released version should be downloaded and installed for use.

For Windows users, there is a juliaup program for managing the installation of Julia.

The base Julia provides a command-line interface, or REPL (read-evaluate-parse).

69.3 Basic interactive usage

Once installed, Julia can be started by clicking on an icon or typing julia at the command line. Either will open a command line interface for a user to interact with a Julia process. The basic workflow is easy: commands are typed then sent to a Julia process when the “return” key is pressed for a complete expression. Then the output is displayed.

A command is typed following the prompt. An example might be 2 + 2. To send the command to the Julia interpreter the “return” key is pressed. A complete expression or expressions will then be parsed and evaluated (executed). If the expression is not complete, julia’s prompt will still accept input to complete the expression. Type 2 + to see. (The expression 2 + is not complete, as the infix operator + expects two arguments, one on its left and one on its right.)

               _
   _       _ _(_)_     |  Documentation: https://docs.julialang.org
  (_)     | (_) (_)    |
   _ _   _| |_  __ _   |  Type "?" for help, "]?" for Pkg help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 1.7.0 (2021-11-30)
 _/ |\__'_|_|_|\__'_|  |  Official https://julialang.org/ release
|__/                   |

julia> 2 + 2
4

Above, julia> is the prompt. These notes will not include the prompt, so that copying-and-pasting can be more easily used. Input and output cells display similarly, though with differences in coloring. For example:

2 + 2

While many prefer a command line for interacting with Julia, when learning a notebook interfaces is suggested. (An IDE like Julia for Visual Studio Code might be preferred for experienced programmers). In Julia interfaces, we describe two different notebook interfaces that are available through add-on packages.

69.4 Add-on packages

Julia is well on its way towards 10,000 external add-on packages that enhance the offerings of base Julia. We refer to one, CalculusWithJulia, that is designed to accompany these notes. Installation notes are available.

In Julia graphics are provided only by add-on packages – there is no built-in graphing. This is the case under Pluto or Jupyter or the command line.

In these notes, we use the Plots package and its default backend. The Plots package provides a common interface to several different backends; this choice is easily changed. The gr backend is used in these notes, though for interactive use the Plotly backend has advantages; for more complicated graphics, pyplot has some advantages; for publication PGFPlotsX has advantages.

The package, if installed, is loaded as any other package:

using Plots

With that in hand, to make a graph of a function over a range, we follow this pattern:

plot(sin, 0, 2pi)