Getting Started with Sage

When you use any of the help commands, the normal contents of the terminal will be replaced by a help screen, which looks like this:

Use the arrows to scroll up and down. Use the Spacebar to page down, and the b key to page up. Press q to leave the help screen and return to the command line. If you want to see the documentation and the source code for the function (if the code is available), type two question marks after the function name:

sage: exp??

Finally, to see the complete class documentation, use the help function:

sage: help(exp)

Command history

The Sage command line has a number of built-in shortcuts that help you work more efficiently. Most of these will be familiar to people who have worked with UNIX-like command line interfaces. We have already seen that you can use the Up arrow on your keyboard to scroll through commands that you have previously entered. To see a list of everything you have typed in this session, type %hist at the command prompt.

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Getting Started with Sage

Interactivelytracingexecution

Only the interactive shell allows you to trace the execution of a command interactively. Use the trace function, which accepts a string that contains a Sage command. For example, to trace the execution of the following exp function:

sage: trace("exp(1.0)")

This command starts the Python debugger, which gives you the ipdb> prompt. To step through execution of the function, type step (or just s) at the prompt and press Enter. Type ? to get help on other commands you can use in the debugger. Type quit (or just q) to quit the debugger and return to the Sage command line. A typical session looks like this:

Usingthenotebookinterface

The notebook interface is a more flexible way to work with Sage. Your calculations and the resulting numbers and plots can be saved together in a worksheet. You can add headings and text to document what you've done. In Chapter 10, we'll learn how to use LaTeX to typeset mathematical expressions right in a worksheet.

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Chapter 3

Startingthenotebookinterface

There are several ways to start the notebook interface. If you are running Sage in a virtual machine on Windows, double-click on the icon labelled Sage Notebook. If you are starting Sage from the command line, you can use the –notebook option to start Sage and launch the notebook interface. If you already have the Sage interactive shell running, use the notebook() function to start the notebook interface:

sage: notebook()

If a web browser doesn't open automatically, manually start the web browser and go to http://localhost:8000.

If this is your first time running the notebook interface, follow the prompts in the terminal to enter a password for the administrative account.

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Getting Started with Sage

When you have entered a password, you will see a screen that allows you to log in. Log in using the name and password you just created.

Once you have logged in, you will see the home page for the notebook interface:

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Chapter 3

You can create a new worksheet by clicking the New Worksheet link. When prompted, enter a name in the dialog box. The blank worksheet should look like this:

You can access many powerful features of the notebook interface from this page:

The six tabs towards the right side of the screen allow you to perform other operations:

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Getting Started with Sage

Timeforaction–doingcalculationswiththenotebookinterface

Now, we will use the Notebook interface to repeat the calculations that we did with the interactive shell. We will add some text to document what we've done.

1. Define variables.

The empty white box in the middle of the worksheet is an input cell. Click in the input cell and type in the following text:

To evaluate the cell, press Shift-Enter or click the evaluate link, which is found just below the bottom-left corner of the input cell. As soon as the code executes, an empty input cell appears on the screen below the previous cell. The screen will look like this:

2. Perform a calculation.

You can also insert an empty input cell by moving the cursor into the blank space above or below an existing cell. When a thin, solid bar appears in the blank space, click to insert a new input cell. Enter the following code in the next input cell:

v0 * exp(-t / tau)

Click the evaluate link or press Shift-Enter to execute the code. The result will appear below the input box.

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Chapter 3

3.Add documentation.

Let's add a text field to document what we've done. Move the mouse cursor to the empty space just above the first input box. As your mouse enters this area, a thin, solid bar will appear. Hold down the Shift key and click on this rectangle to insert a new text cell. The text cell will include a graphical editor that allows you to enter text and apply HTML formatting. Choose Heading 1 from the menu at the upper left corner of the editor, and type RC Circuit Analysis into the box. Click the Save Changes button to exit the editor.

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Getting Started with Sage

4.Save your work.

Click the Save button at the top-right corner of the worksheet. If you are done with this notebook, click Save & quit.

What just happened?

We repeated the calculation that we performed earlier. This time, we were able to create a single document that contains calculations, results, and documentation. We made use of comments in the input cells to note the units for each value (you can also use comments on the command line). A # sign indicates the beginning of a comment. Sage ignores anything on the line after the #. Get in the habit of using comments to remind yourself how the code works. As in the interactive shell, no output is displayed when a value is assigned to a variable. Only the last line of an input cell will produce output on the screen. We'll see how to produce more output in the next section.

Gettinghelpinthenotebookinterface

To get help with the notebook interface, click the Help link in the upper-right corner of the notebook window. To get help on a command or function, type the command name in an empty input cell, followed by a ?. Press Tab, or evaluate the cell, to see the documentation. You can also type the command name followed by ?? to see the source code. Another option is to type help(command), which will result in a link that you can click to open the documentation in a new tab or window. To search the documentation, type search_ doc("my query") in an empty input cell and evaluate the cell. You can also search the source code by using search_src("my query").

Workingwithcells

The example showed some of the basic commands that can be used to edit worksheets.

The following shortcuts are useful for working with cells:

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