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# FAQ: Using Sage

## How do I get started?

You can try out Sage without downloading anything. Go to http://www.sagenb.org and set up a free account. If you log in, you will be working on a free Sage notebook server that will work identically to the one you get with Sage. To download a pre-built binary Sage distribution, visit the page http://www.sagemath.org/download.html and click on the link for the binary for your operating system. The source code of Sage is also available for you to download and use. Go to http://www.sagemath.org/download-source.html to download the tar archive for any release of Sage. Previous releases of Sage are available at http://www.sagemath.org/src-old.

The Sage notebook runs within a web browser. You can run Sage in a browser that is not the system default. To do so, issue the following command

    env SAGE_BROWSER=opera /usr/bin/sage -notebook

either from the command prompt or as a menu command for Sage.

## What are Sage’s prerequisites?

Most of the dependencies of Sage are shipped with Sage itself. In most cases, you can download a pre-built binary and use that without installing any dependencies. If you use Windows, you will need to install VirtualBox, which can be downloaded from the page http://www.virtualbox.org/wiki/Downloads. After installing VirtualBox, you need to download a VirtualBox distribution of Sage available at http://www.sagemath.org/download-windows.html. Ensure you follow the instructions at that page. Now you can start the Sage virtual machine using the VirtualBox software, wait for the virtual machine to boot up, then type `notebook` at the prompt.

You can get the complete source for Sage to compile it on your own Linux or Mac OS X system. Sage lives in an isolated directory and does not interfere with your surrounding system. It ships together with everything necessary to develop Sage, the source code, all its dependencies and the complete changelog. On Linux systems like Debian/Ubuntu, you may have to install the `build essential` package and the `m4` macro processor. Your system needs to have a working C compiler if you want to compile Sage from source. On Debian/Ubuntu, you can install these prerequisites as follows:

    sudo apt-get install build-essential m4

If you have a multi-core system, you can opt for a parallel build of Sage. The command

    export MAKE='make -j8'

will enable 8 threads for parts of the build that support parallelism. Change the number 8 as appropriate to suit the number of cores on your system.

## How to get Sage’s Python to recognize my system’s Tcl/Tk install?

It may be that you have Tcl/Tk installed and that your system’s Python recognizes it but Sage’s Python does not. To fix that, install the tcl/tk development library. On Ubuntu, this is the command

    sudo apt-get install tk8.5-dev

or something along that line. Next, reinstall Sage’s Python:

    sage -f python

This will pick up the tcl/tk library automatically. After successfully reinstalling Sage’s Python, from within the Sage command line interface, issue these commands:

    import _tkinter
    import Tkinter

If they do not raise an `ImportError` then it worked.

## How do I import Sage into a Python script?

You can import Sage as a library in a Python script. One caveat is that you need to run that Python script using the version of Python that is bundled with Sage; currently Python 2.6.x. To import Sage, put the following in your Python script:

    from sage.all import *

When you want to run your script, you need to invoke Sage with the option `-python` which would run your script using the version of Python that comes with Sage. For example, if Sage is in your `PATH` variable then you can do this:

    sage -python /path/to/my/script.py

Another way is to write a Sage script and run that script using Sage itself. A Sage script has the file extension `.sage` and is more or less a Python script but uses Sage-specific functions and commands. You can then run that Sage script like so:

    sage /path/to/my/script.sage

This will take care of loading the necessary environment variables and default imports for you.

## How can I reload a Python script in a Sage session?

You can load a Python script in a Sage session with the command load. For example, we could use Sage to import a file called simple.py with:

    load("simple.py")

and repeat this command every time that we change the file simple.py. However, if we type:

    attach("simple.py")

every change applied to the file simple.py will be automatically updated in Sage.

## Can I use Sage with Python 3.x?

Currently, no. Sage depends on the SciPy stack of Python numerical and scientific packages. As of 2010, SciPy still uses Python 2.x. So until SciPy is ported to run with Python 3.x and Cython supports Python 3.x, Sage will continue to use Python 2.x.

## I’m seeing an error about “Permission denied” on a file called “sage-flags.txt”.

When sage is built from source, it keeps track of what special instructions your CPU supports (such as SSE2) and records these. This is so that if you try running the code on a different machine, which does not support these extra instructions, you get a sensible error message instead of a segfault or illegal instruction. Since this should be stored with Sage itself (as opposed to a user’s `.sage` directory), it has to be created by someone with the appropriate permissions. So if you are seeing something like this

    Traceback (most recent call last):
      File "/usr/local/sage-4.0.2/local/bin/sage-location", line 174, in <module>
        t, R = install_moved()
      File "/usr/local/sage-4.0.2/local/bin/sage-location", line 18, in install_moved
        write_flags_file()
      File "/usr/local/sage-4.0.2/local/bin/sage-location", line 82, in write_flags_file
        open(flags_file,'w').write(get_flags_info())
    IOError: [Errno 13] Permission denied:
      '/usr/local/sage-4.0.2/local/lib/sage-flags.txt'

it probably means that you compiled/installed Sage as one user, but have not run it to let it generate the `sage-flags.txt` file. Just run Sage one time as whatever user installed it and this problem should go away. This would also be easy to fix by having Sage run once as part of the install process; see trac ticket #6375 for this fix.

## I downloaded a Sage binary and it crashes on startup with “Illegal instruction”. What can I do?

One way to fix this is to build Sage entirely from source. Another option is to fix your Sage installation by rebuilding MPIR and ATLAS by typing the following from the `SAGE_ROOT` of your Sage installation directory and wait about 15 to 20 minutes:

    rm spkg/installed/mpir* spkg/installed/atlas*
    make

It is possible that the binaries have been built for a newer architecture than what you have. Nobody has yet figured out how to build Sage in such a way that MPIR and ATLAS work on all hardware. This will eventually get fixed. Any help is appreciated.

## I used Debian/Ubuntu to install Sage 3.0.5 and that version is giving lots of errors. What can I do?

The version of Sage, i.e. Sage version 3.0.5, that is available through `apt-get` in Debian and Ubuntu is very old. No one has yet found time to update the Debian/Ubuntu version of Sage. Any help is greatly appreciated. You should download the latest version of Sage from the download page. If you would like to help with updating the Debian/Ubuntu version of Sage, please email the sage-devel mailing list.

## Should I use the official version or development version?

You are encouraged to use the latest official version of Sage. Development versions are frequently announced on the sage-devel and sage-release mailing lists. An easy way of helping out with Sage development is to download the latest development release, compile it on your system, run all doctests, and report any compilation errors or doctest failures.

## Is Sage difficult to learn?

Basic features of Sage should be as easy to learn as learning the basics of Python. Numerous tutorials are available online to help you learn Sage. To get the most out of Sage, you are encouraged to learn some features of the Python programming language. Here is an incomplete list of resources on Python. Further resources can be found by a web search.

- Building Skills in Python by Steven F. Lott
- Dive into Python by Mark Pilgrim
- How to Think Like a Computer Scientist by Jeffrey Elkner, Allen B. Downey, and Chris Meyers
- Official Python Tutorial
- Python home page and the Python standard documentation

## Can I do X in Sage?

You are encouraged to use Sage’s tab autocompletion. Just type a few characters, hit the tab key, and see if the command you want appears in the list of tab autocompletion. If you have a command called `mycmd`, then type `mycmd.` and hit the tab key to get a list of functionalities that are supported by that command. To read the documentation of `mycmd`, type `mycmd?` and press the enter key to read the documentation for that command. Similarly, type `mycmd??` and hit the enter key to get the source code of that command. You are also encouraged to search through the source code and documentation of the Sage library. To search through the source code of the Sage library, use the command `search_src("<search-keyword>")` where you should replace `<search-keyword>` with the key words you are looking for. Also, you can search through the documentation of the Sage library using the command `search_doc("<search-keyword>")`.

## What exactly does Sage do when I type “0.6**2”?

When you type “0.6**2” in Python, it returns something like 0.35999999999999999. But when you do the same in Sage it returns 0.360000000000000. To understand why Python behaves as it does, see the Python Tutorial, especially the chapter “Floating Point Arithmetic: Issues and Limitations”. What Sage does is “preparse” the input and transforms it like this:

    sage: preparse("0.6**2")
    "RealNumber('0.6')**Integer(2)"

So what is actually run is:

    RealNumber('0.6')**Integer(2)

The Sage developers (in fact, Carl Witty) decided that Sage floating point numbers should by default print only the known correct decimal digits, when possible, thus skirting the problem that Python has. This decision has its pros and cons. Note that `RealNumber` and `Integer` are Sage specific, so you would not be able to just type the above into Python and expect it to work without first an import statement such as:

    from sage.all import RealNumber, Integer, preparse

## Why is Sage’s command history different from Magma’s?

Using Sage, you are missing a feature of the Magma command line interface. In Magma, if you enter a line found in history using up arrow key and then press down arrow key, then the next line in history is fetched. This feature allows you to fetch as many successive lines in history as you like. However, Sage does not have a similar feature. The IPython command prompt uses the readline library (via pyreadline), which evidently does not support this feature. Magma has its own custom “readline-like” library, which does support this feature. (Since so many people have requested this feature, if anybody can figure out how to implement it, then such an implementation would certainly be welcome!)

## I have type issues using SciPy, cvxopt or NumPy from Sage.

You are using SciPy or cvxopt or NumPy from Sage and you get type errors, e.g.

    TypeError: function not supported for these types, and can't coerce safely to supported types.

When you type in numbers into Sage, the pre-processor converts them to a base ring, which you can see by doing:

    sage: preparse("stats.uniform(0,15).ppf([0.5,0.7])")
    "stats.uniform(Integer(0),Integer(15)).ppf([RealNumber('0.5'),RealNumber('0.7')])"

Unfortunately, NumPy support of these advanced Sage types like `Integer` or `RealNumber` is not yet at 100%. As a solution, redefine `RealNumber` and/or `Integer` to change the behavior of the Sage preparser, so decimal literals are floats instead of Sage arbitrary precision real numbers, and integer literals are Python ints. For example:

    sage: RealNumber = float; Integer = int
    sage: from scipy import stats
    sage: stats.ttest_ind(list([1,2,3,4,5]),list([2,3,4,5,.6]))
    (array(0.07675295564533369), 0.94070490247380478)
    sage: stats.uniform(0,15).ppf([0.5,0.7])
    array([  7.5,  10.5])

Alternatively, be explicit about data types, e.g.

    sage: from scipy import stats
    sage: stats.uniform(int(0),int(15)).ppf([float(0.5),float(0.7)])
    array([  7.5,  10.5])

As a third alternative, use the raw suffix:

    sage: from scipy import stats
    sage: stats.uniform(0r,15r).ppf([0.5r,0.7r])
    array([  7.5,  10.5])

You can also disable the preprocessor in your code via `preparse(False)`. You can may start IPython alone from the command line `sage -ipython` which does not pre-load anything Sage-specific. Or switching the Notebook language to “Python”.

## How do I save an object so I don’t have to compute it each time I open a worksheet?

The `save` and `load` commands will save and load an object, respectively. In the notebook, the `DATA` variable is the location of the data storage area of the worksheet. To save the object `my_stuff` in a worksheet, you could do

    save(my_stuff, DATA + "my_stuff")

and to reload it, you would just do

    my_stuff = load(DATA + "my_stuff")

## I get an error from jsMath or the math symbols don’t look right when displaying in the notebook.

If you see the error

    It looks like jsMath failed to set up properly (error code -7). I will try to keep going, but it could get ugly.

you have not installed the TeX fonts which help jsMath render beautiful typeset mathematics. To get the nice TeX display with jsMath, please download a set of fonts from here from http://www.math.union.edu/~dpvc/jsMath/download/jsMath-fonts.html. If you are on Linux/Unix, ignore the instructions on the page and just unzip the fonts into your `~/.fonts` directory. You can also install the `jsmath-fonts` package.

## Does Sage contain a function similar to Mathematica’s ToCharacterCode[]?

You might want to convert ASCII characters such as “Big Mac” to ASCII numerals for further processing. In Sage and Python, you can use `ord`, e.g.

    sage: map(ord, "abcde")
    [97, 98, 99, 100, 101]
    sage: map(ord, "Big Mac")
    [66, 105, 103, 32, 77, 97, 99]

## Can I make Sage automatically execute commands on startup?

Yes, just make a file `$HOME/.sage/init.sage` and it will be executed any time you start Sage. This assumes that the Sage environment variable `DOT_SAGE` points to the hidden directory `$HOME/.sage`, which by default is the case.

## My Sage upgrade failed with missing gmp symbols on OSX 10.4. What can I do?

Moving a Sage install on Mac OS X 10.4 and then upgrading anything that is linked against NTL leads to link errors due to missing gmp symbols. The problem is the link mode with which the dynamic NTL is created. There is have a fix, but it still being verified that it really fixes the issue. Everything that is linked against NTL needs to be recompiled, i.e. singular and cremona at the moment. To add to the confusion: This is not an issue on Mac OS X 10.5. A fix for this issue went into Sage 2.8.15, so please report if you see this with a more current Sage release.

## When I compile Sage my computer beeps and shuts down or hangs.

Compiling Sage is quite taxing on the CPU. The above behavior usually indicates that your computer has overheated. In many cases this can be fixed by cleaning the CPU fan and assuring proper ventilation of the system. Please ask your system administrator or a professional to do this in case you have never done this. Such hardware maintenance, if not performed by a skilled professional, you can potentially damage your system.

For Linux users, if you suspect that the compilation fails because of a resource issue, a fix might be to edit your `/etc/inittab` so that Linux boots into run level 3. The file `/etc/inittab` usually contains something similar to the following snippet:

    #   0 - halt (Do NOT set initdefault to this)
    #   1 - Single user mode
    #   2 - Multiuser, without NFS (The same as 3, if you do not have
    #   networking)
    #   3 - Full multiuser mode
    #   4 - unused
    #   5 - X11
    #   6 - reboot (Do NOT set initdefault to this)
    #
    id:5:initdefault:

which directs your Linux distribution to boot into a graphical login screen. Comment out the line `id:5:initdefault:` and add the line `id:3:initdefault:`, so that you now have something like:

    #   0 - halt (Do NOT set initdefault to this)
    #   1 - Single user mode
    #   2 - Multiuser, without NFS (The same as 3, if you do not have
    #   networking)
    #   3 - Full multiuser mode
    #   4 - unused
    #   5 - X11
    #   6 - reboot (Do NOT set initdefault to this)
    #
    # id:5:initdefault:
    id:3:initdefault:

Now if you reboot your system, you will be greeted with a text based login screen. This allows you to log into your system with a text based session from within a virtual terminal. A text based session usually does not consume as much system resources as would be the case with a graphical session. Then build your Sage source distribution from within your text based session. You need to make sure that you can first restore your graphical session, before you attempt to log into a text based session.

## When I run doctests on Mac OS X I see the messages with “malloc”, but in the end Sage reports that everything went fine.

The “malloc” messages you refer to might be something such as the following:

    sage -t  src/sage/libs/pari/gen.pyx
    python(4563) malloc: *** vm_allocate(size=4096000000) failed (error code=3)
    python(4563) malloc: *** error: can't allocate region
    python(4563) malloc: *** set a breakpoint in szone_error to debug

The issue above is not a doctest failure. It is an error message printed by the system and it is exactly what one expects to see. In that particular doctest, we try to allocate a very large list in Pari that does not fit into physical memory (it is at least 100GB in size). So Mac OS X tells you that it could not allocate a chunk of memory roughly 4 GB in size, which is expected, if you are using Sage on a 32-bit version of OS X and you have compiled Sage in 32-bit bit mode or your binary Sage distribution is 32-bit.

## Sage 2.9 and higher fails compiling ATLAS on Linux. How can I fix this?

The most likely cause is enabled power management. Disabling it should fix the problem. Depending on your flavor of distribution, this might either be possible with some nice GUI tool or not. On the command line do the following as root for each CPU you have:

    /usr/bin/cpufreq-selector -g performance -c #number CPU

On Ubuntu, try disabling “Power Manager” via

    System --> Preferences --> Sessions

under the “Startup Programs” or using `cpufreq-set` via the command line.

## Sage fails with the error message “restore segment prot after reloc: Permission denied”. What is wrong?

The problem is related to SELinux. See this page for some tips to fix this: http://www.ittvis.com/services/techtip.asp?ttid=3092. We are currently tracking this issue at ticket #480.

## When I start Sage, SELinux complains that “/path/to/libpari-gmp.so.2” requires text-relocation. How can I fix it?

The problem can be fixed by running the following command:

    chcon -t textrel_shlib_t /path/to/libpari-gmp.so.2

## Upgrading Sage went fine, but now the banner still shows the old version. How can I fix this?

The banner is stored and not computed at every new start of Sage. If it has not been updated, this should not prevent Sage to run correctly. Type `banner()` in a Sage session to check the real version. If you want the correct banner, you need to build Sage again by typing `make build` in a terminal.

## How do I run sage in daemon mode, i.e. as a service?

We currently do not have a ready-to-go solution. There are several possibilities. Use `screen`, `nohup` or `disown`. We are tracking the issue at ticket #381 so stay tuned.

## I am using Mac OS X. Where do I put the jsMath “font” directory to eliminate the red box?

See http://www.math.union.edu/~dpvc/jsMath/download/jsMath-fonts.html where it says:

    For Mac OS X users: download and unpack the archive, then drag
    the fonts to your Library/Fonts folder (or to the FontBook, or
    just double-click them and press the "install" button).

## The show command for plotting 3-D objects does not work.

The default live 3-D plotting for Sage 6.4+ uses Jmol/JSmol for viewing. From the command line the Jmol Java application is used, and for in browser viewing either pure javascript or a Java applet is used. By default in browsers pure javascript is used to avoid the problems with some browsers that do not support java applet plugins (namely Chrome). On each browser worksheet there is a checkbox which must be checked before a 3-D plot is generated if the user wants to use the Java applet (the applet is a little faster with complex plots).

The most likely reason for a malfunction is that you do not have a Java Run Time Environment (JRE) installed or you have one older than version 1.7. If things work from the command line another possibility is that your browser does not have the proper plugin to support Java applets (at present, 2014, plugins do not work with most versions of Chrome). Make sure you have installed either the IcedTea browser plugin (for linux see your package manager), see: IcedTea, or the Oracle Java plugin see: Java.

If you are using a Sage server over the web and even javascript rendering does not work, you may have a problem with your browser’s javascript engine or have it turned off.

## May I use Sage tools in a commercial environment?

Yes! Absolutely! Basically the only constraint is that if you make changes to Sage itself and redistribute this changed version of Sage publicly, then you must make these changes available to us so that we can put them into the standard version of Sage (if we want). Otherwise, you are free to use as many copies of Sage as you want completely for free to make money, etc. without paying any license fees at all.

## I want to write some Cython code that uses finite field arithmetic but “cimport sage.rings.finite_field_givaro” fails. What can I do?

You need to give hints to Sage so that it uses C++ (both Givaro and NTL are C++ libraries), and it also needs the GMP and STDC C++ libraries. Here is a small example:

    # These comments are hints to Sage/Pyrex about the compiler and
    # libraries needed for the Givaro library:
    #
    #clang c++
    #clib givaro gmpxx gmp m stdc++
    cimport sage.rings.finite_field_givaro
    # Construct a finite field of order 11.
    cdef sage.rings.finite_field_givaro.FiniteField_givaro K
    K = sage.rings.finite_field_givaro.FiniteField_givaro(11)
    print "K is a", type(K)
    print "K cardinality =", K.cardinality()
    # Construct two values in the field:
    cdef sage.rings.finite_field_givaro.FiniteField_givaroElement x
    cdef sage.rings.finite_field_givaro.FiniteField_givaroElement y
    x = K(3)
    y = K(6)
    print "x is a", type(x)
    print "x =", x
    print "y =", y
    print "x has multiplicative order =", x.multiplicative_order()
    print "y has multiplicative order =", y.multiplicative_order()
    print "x*y =", x*y
    # Show that x behaves like a finite field element:
    for i in range(1, x.multiplicative_order() + 1):
        print i, x**i
    assert x*(1/x) == K.one_element()

To find out more, type

    sage.rings.finite_field_givaro.FiniteField_givaro.

at the Sage prompt and hit tab, then use `??` to get more information on each function. For example:

    sage.rings.finite_field_givaro.FiniteField_givaro.one_element??

tells you more about the multiplicative unit element in the finite field.

## I’m getting weird build failures on Mac OS X. How do I fix this?

Search the build log (install.log) to see if you are getting the following log message:

    fork: Resource temporarily unavailable.

If so, try the following. Create (or edit) `/etc/launchd.conf` and include the following:

    limit maxproc 512 2048

then reboot. See this page for more details.

## How do I use the bitwise XOR operator in Sage?

The exclusive or operator in Sage is `^^`. This also works for the inplace operator `^^=`:

    sage: 3^^2
    1
    sage: a = 2
    sage: a ^^= 8
    sage: a
    10

If you define two variables and then evaluate as follows:

    sage: a = 5; b = 8
    sage: a.__xor__(b), 13
    (13, 13)

You can also do

    sage: (5).__xor__(8)
    13

The parentheses are necessary so that Sage does not think you have a real number. There are several ways to define a function:

    sage: xor = lambda x, y: x.__xor__(y)
    sage: xor(3, 8)
    11

Another option, which sneaks around the Sage preparser, is

    sage: def xor(a, b):
    ...       return eval("%s^%s" % (a, b))
    ...
    sage: xor(3, 8)
    11

You can also turn off the Sage preparser with `preparser(False)`, then `^` will work just like in Python. You can later turn on the preparser with `preparser(True)`. That only works in command line Sage. In a notebook, switch to Python mode.

## When I try to use LaTeX in the notebook, it says it cannot find fullpage.sty.

The general—but perhaps not very helpful—answer is that you need to install `fullpage.sty` into a directory searched by TeX. On Ubuntu (and probably many other Linux distributions), you should install the `texlive-latex-extra` package. If that is not available, try installing the `tetex-extra package`. If you are using Mac OS X, you will have to use whatever TeX distribution you use to get `fullpage.sty` (if you use MacTeX, it is likely already installed). If you are using the VirtualBox image on Windows, you will need to log into the VirtualBox image and install `texlive-latex-extra` there.

## With objects a and b and a function f, I accidentally typed f(a) = b instead of f(a) == b. This returned a TypeError (as expected), but also deleted the object a. Why?

It is because of how functions are defined in Sage with the `f(x) = expr` notation using the preparser. Also notice that if you make this mistake inside of an `if` statement, you will get a `SyntaxError` before anything else goes wrong. So in this case, there is no problem.

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