template/book/syntax_exercises/009.md

# Exercise 9: Cross-referencing content

In this exercise, you will learn how to create references to other parts of your book, such as chapters, sections, equations, tables and figures, as well as links.

::::::{topic} Exercise objective
Can you create internal references to other sections, equations, tables, figures, and links?
::::::

```{tip}
Referencing elements properly ensures that readers can navigate your book more easily. More details can be found in the [JupyterBook documentation](https://jupyterbook.org/en/stable/content/references.html).
```

## 1. Referencing a Chapter or Section

1. Open a new or existing Markdown file where you want to add a reference.
2. Let's start with the simplest way to create a reference to another chapter. This is by directly linking it through the file path as shown in the following syntax:

```md
[Text to display](path/to/file.md)
```

For example, if you want to link to Exercise 7, you can write:

```md
[Go to Exercise 7](../exercises/007.md)
```
3. Try out another way of referencing by using a target header. Navigate to the chapter or section you want to reference and assign it an identifier using `{ref}` as shown in the example below. This could be either in the same markdown file, or a different file altogether.

```md
(exercise_1)=
# Exercise 1: First file edit

Let's start with the most basic edit: add some text to a file and see that the website is updated...
```
4. Now, let's explore three different ways to reference this section or chapter! For the first method, we use the standard title text by calling the identifier as follows:

  ```md
  My favourite exercise was {ref}`exercise_1`.
  ```
  This will display: My favourite exercise was {ref}`exercise_1`.


5. For the second method, we want to refer to the section using a custom title text. Try this out by placing the text that you want to be displayed within the `` and calling the identifier within the <> as follows:

  ```md
  My favourite exercise was {ref}`the first one <exercise_1>`.
  ```
  This will display: My favourite exercise was {ref}`the first one <exercise_1>`.


6. The final method uses markdown syntax to also display a custom title text. Refer to the desired section once again, this time by putting the custom text within the [] and calling the identifier within the <> as shown below:


  ```md
  My favourite exercise was [this one](exercise_1).
  ```
  This will display: My favourite exercise was [this one](exercise_1).

These three referencing methods can also be used for referencing equations, tables and figures.

## 2. Referencing an Equation

7. Now we will test our knowledge using an equation. Similar to the code below, create an equation using $$ and identify it using a label within the brackets.


  ```md

 $$ F = m \cdot a$$ (eq:Newton)

  ```

This will display as follows:

 $$ F = m \cdot a$$ (eq:Newton)

8. In this step, we will use the three referencing methods discussed above to reference this equation as follows:


```md
Refer to Equation {eq}`eq:Newton`
Refer to the {eq}'above equation <eq:Newton>'
Refer to [this equation](eq:Newton)
```
These will display as:

Refer to Equation {eq}`eq:Newton`
Refer to the {eq}'above equation <eq:Newton>'
Refer to [this equation](eq:Newton)


## 3. Referencing a Table

To reference a table, assign a label when defining it:

```md
    ```{table} Example Table
    :label: tab-example
    | Column 1 | Column 2 |
    |----------|----------|
    | A        | B        |
    ```
```

And refer to it using `{numref}`:

```md
Table {numref}`tab-example`
```


## 4. Referencing a Figure

To reference a figure, label it when inserting it:

```md
    ```{figure} figures/example.png
    ---
    width: 80%
    align: center
    name: fig-example
    ---
    Example figure.
    ```
```

And refer to it using `{numref}`:

```md
Figure {numref}`fig-example`
```

## 5. Referencing a Link

To reference a link, use the following syntax:

```md
[Text to display](https://teachbooks.github.io/template/)
```
For example, you can write:

```md
Here is the [link to the template](https://teachbooks.github.io/template/).
```

This wil display: Here is the [link to the template](https://teachbooks.github.io/template/).




## 6. Commit Your Changes

1. Once you have added your references, commit your changes to the repository.
2. Click the green `Commit changes` button.
3. Add a commit message.
4. View your changes using the `Actions` tab and check if they appear correctly.

```{admonition} Check your understanding
:class: note

Before moving on to the next exercise, make sure you understand the following:
- How do you reference another chapter or section?
- How do you create a reference to an equation, table or figure in your book?
- How do you reference a link?