tutorial.txt

.. _tutorial:

========
Tutorial
========

.. role:: input(strong)

Introduction
============

SymPy is a Python library for symbolic mathematics. It aims to become a
full-featured computer algebra system (CAS) while keeping the code as simple as
possible in order to be comprehensible and easily extensible.  SymPy is written
entirely in Python and does not require any external libraries.

This tutorial gives an overview and introduction to SymPy.
Read this to have an idea what SymPy can do for you (and how) and if you want
to know more, read the
:ref:`SymPy User's Guide <guide>`,
:ref:`SymPy Modules Reference <module-docs>`.
or the `sources
<https://github.com/sympy/sympy/>`_ directly.

First Steps with SymPy
======================

The easiest way to download it is to go to
http://code.google.com/p/sympy/ and
download the latest tarball from the Featured Downloads:

.. image:: figures/featured-downloads.png

Unpack it:

.. parsed-literal::

    $ :input:`tar xzf sympy-0.5.12.tar.gz`

and try it from a Python intepreter:

.. parsed-literal::

    $ cd sympy-0.5.12
    $ python
    Python 2.4.4 (#2, Jan  3 2008, 13:36:28)
    [GCC 4.2.3 20071123 (prerelease) (Debian 4.2.2-4)] on linux2
    Type "help", "copyright", "credits" or "license" for more information.
    >>> from sympy import Symbol, cos
    >>> x = Symbol("x")
    >>> (1/cos(x)).series(x, 0, 10)
    1 + x**2/2 + 5*x**4/24 + 61*x**6/720 + 277*x**8/8064 + O(x**10)

You can use SymPy as shown above and this is indeed the recommended way if you
use it in your program. You can also install it using ``./setup.py install`` as
any other Python module, or just install a package in your favourite Linux
distribution, e.g.:

.. topic:: Installing SymPy in Debian

  .. parsed-literal::

    $ :input:`sudo apt-get install python-sympy`
    Reading package lists... Done
    Building dependency tree
    Reading state information... Done
    The following NEW packages will be installed:
      python-sympy
    0 upgraded, 1 newly installed, 0 to remove and 18 not upgraded.
    Need to get 991kB of archives.
    After this operation, 5976kB of additional disk space will be used.
    Get:1 http://ftp.cz.debian.org unstable/main python-sympy 0.5.12-1 [991kB]
    Fetched 991kB in 2s (361kB/s)
    Selecting previously deselected package python-sympy.
    (Reading database ... 232619 files and directories currently installed.)
    Unpacking python-sympy (from .../python-sympy_0.5.12-1_all.deb) ...
    Setting up python-sympy (0.5.12-1) ...


For other means how to install SymPy, consult the  Downloads_ tab on the
SymPy's webpage.

.. _Downloads: http://code.google.com/p/sympy/wiki/DownloadInstallation?tm=2


isympy Console
--------------

For experimenting with new features, or when figuring out how to do things, you
can use our special wrapper around IPython called ``isympy`` (located in
``bin/isympy`` if you are running from the source directory) which is just a
standard python shell that has already imported the relevant sympy modules and
defined the symbols x, y, z and some other things:

.. parsed-literal::

    $ :input:`cd sympy`
    $ :input:`./bin/isympy`
IPython console for SymPy 0.6.7-git (Python 2.7.1) (ground types: gmpy)

These commands were executed:
>>> from __future__ import division
>>> from sympy import *
>>> x, y, z, t = symbols('x y z t')
>>> k, m, n = symbols('k m n', integer=True)
>>> f, g, h = symbols('f g h', cls=Function)

Documentation can be found at http://www.sympy.org

    In [1]: input:`(1/cos(x)).series(x, 0, 10)`
    Out[1]:
         2      4       6        8
        x    5*x    61*x    277*x
    1 + ── + ──── + ───── + ────── + O(x**10)
        2     24     720     8064

.. note::

    Commands entered by you are bold. Thus what we did in 3 lines in a regular
    Python interpeter can be done in 1 line in isympy.


Using SymPy as a calculator
---------------------------

Sympy has three built-in numeric types: Float, Rational and Integer.

The Rational class represents a rational number as a pair of two Integers: the numerator and the denominator, so Rational(1,2) represents 1/2, Rational(5,2) 5/2 and so on.

::

    >>> from sympy import *
    >>> a = Rational(1,2)

    >>> a
    1/2

    >>> a*2
    1

    >>> Rational(2)**50/Rational(10)**50
    1/88817841970012523233890533447265625


proceed with caution while working with python int's since they truncate
integer division, and that's why::

   >>> 1/2
   0

   >>> 1.0/2
   0.5

You can however do::

  >>> from __future__ import division

  >>> 1/2 #doctest: +SKIP
  0.5

True division is going to be standard in python3k and ``isympy`` does that too.

We also have some special constants, like e and pi, that are treated as symbols
(1+pi won't evaluate to something numeric, rather it will remain as 1+pi), and
have arbitrary precission::

    >>> pi**2
    pi**2

    >>> pi.evalf()
    3.14159265358979

    >>> (pi+exp(1)).evalf()
    5.85987448204884

as you see, evalf evaluates the expression to a floating-point number

There is also a class representing mathematical infinity, called ``oo``::

    >>> oo > 99999
    True
    >>> oo + 1
    oo

Symbols
-------

In contrast to other Computer Algebra Systems, in SymPy you have to declare
symbolic variables explicitly::

    >>> from sympy import *
    >>> x = Symbol('x')
    >>> y = Symbol('y')

Then you can play with them::

    >>> x+y+x-y
    2*x

    >>> (x+y)**2
    (x + y)**2

    >>> ((x+y)**2).expand()
    x**2 + 2*x*y + y**2

And substitute them for other symbols or numbers using ``subs(old, new)``::

    >>> ((x+y)**2).subs(x, 1)
    (y + 1)**2

    >>> ((x+y)**2).subs(x, y)
    4*y**2

For the remainder of the tutorial, we assume that we have run::

    >>> import sys
    >>> oldhook = sys.displayhook
    >>> sys.displayhook = pprint

So that things pretty print.  See the :ref:`printing-tutorial` section below.  If you have a unicode font installed, your output may look a litte different (it will look slightly nicer).

Algebra
=======

For partial fraction decomposition, use ``apart(expr, x)``::

    >>> 1/( (x+2)*(x+1) )
           1
    ---------------
    (x + 1)*(x + 2)

    >>> apart(1/( (x+2)*(x+1) ), x)
        1       1
    - ----- + -----
      x + 2   x + 1

    >>> (x+1)/(x-1)
    x + 1
    -----
    x - 1

    >>> apart((x+1)/(x-1), x)
          2
    1 + -----
        x - 1

To combine things back together, use ``together(expr, x)``::

    >>> together(1/x + 1/y + 1/z)
    x*y + x*z + y*z
    ---------------
         x*y*z

    >>> together(apart((x+1)/(x-1), x), x)
    x + 1
    -----
    x - 1

    >>> together(apart(1/( (x+2)*(x+1) ), x), x)
           1
    ---------------
    (x + 1)*(x + 2)


.. index:: calculus

Calculus
========

.. index:: limits

Limits
------

Limits are easy to use in sympy, they follow the syntax limit(function,
variable, point), so to compute the limit of f(x) as x -> 0, you would issue
limit(f, x, 0)::

   >>> from sympy import *
   >>> x=Symbol("x")
   >>> limit(sin(x)/x, x, 0)
   1

you can also calculate the limit at infinity::

   >>> limit(x, x, oo)
   oo

   >>> limit(1/x, x, oo)
   0

   >>> limit(x**x, x, 0)
   1

for some non-trivial examples on limits, you can read the test file
`test_demidovich.py
<https://github.com/sympy/sympy/blob/master/sympy/series/tests/test_demidovich.py>`_

.. index:: differentiation, diff

Differentiation
---------------

You can differentiate any SymPy expression using ``diff(func, var)``. Examples::

    >>> from sympy import *
    >>> x = Symbol('x')
    >>> diff(sin(x), x)
    cos(x)
    >>> diff(sin(2*x), x)
    2*cos(2*x)

    >>> diff(tan(x), x)
       2
    tan (x) + 1

You can check, that it is correct by::

    >>> limit((tan(x+y)-tan(x))/y, y, 0)
       2
    tan (x) + 1

Higher derivatives can be calculated using the ``diff(func, var, n)`` method::

    >>> diff(sin(2*x), x, 1)
    2*cos(2*x)

    >>> diff(sin(2*x), x, 2)
    -4*sin(2*x)

    >>> diff(sin(2*x), x, 3)
    -8*cos(2*x)


.. index::
    single: series expansion
    single: expansion; series

Series expansion
----------------

Use ``.series(var, point, order)``::

    >>> from sympy import *
    >>> x = Symbol('x')
    >>> cos(x).series(x, 0, 10)
         2    4     6      8
        x    x     x      x
    1 - -- + -- - --- + ----- + O(x**10)
        2    24   720   40320
    >>> (1/cos(x)).series(x, 0, 10)
         2      4       6        8
        x    5*x    61*x    277*x
    1 + -- + ---- + ----- + ------ + O(x**10)
        2     24     720     8064

Another simple example::

    from sympy import Integral, Symbol, pprint

    x = Symbol("x")
    y = Symbol("y")

    e = 1/(x + y)
    s = e.series(x, 0, 5)

    print(s)
    pprint(s)

That should print the following after the execution::

    1/y + x**2*y**(-3) + x**4*y**(-5) - x*y**(-2) - x**3*y**(-4) + O(x**5)
         2    4         3
    1   x    x    x    x
    ─ + ── + ── - ── - ── + O(x**5)
    y    3    5    2    4
        y    y    y    y

.. index:: integration

Integration
-----------

SymPy has support for indefinite and definite integration of transcendental
elementary and special functions via `integrate()` facility, which uses
powerful extended Risch-Norman algorithm and some heuristics and pattern
matching::

    >>> from sympy import *
    >>> x, y = symbols('x,y')

You can integrate elementary functions::

    >>> integrate(6*x**5, x)
     6
    x
    >>> integrate(sin(x), x)
    -cos(x)
    >>> integrate(log(x), x)
    x*log(x) - x
    >>> integrate(2*x + sinh(x), x)
     2
    x  + cosh(x)

Also special functions are handled easily::

    >>> integrate(exp(-x**2)*erf(x), x)
      ____    2
    \/ pi *erf (x)
    --------------
          4

It is possible to compute definite integral::

    >>> integrate(x**3, (x, -1, 1))
    0
    >>> integrate(sin(x), (x, 0, pi/2))
    1
    >>> integrate(cos(x), (x, -pi/2, pi/2))
    2

Also improper integrals are supported as well::

    >>> integrate(exp(-x), (x, 0, oo))
    1
    >>> integrate(log(x), (x, 0, 1))
    -1

.. index::
    single: complex numbers
    single: expansion; complex

Complex numbers
---------------

::

    >>> from sympy import Symbol, exp, I
    >>> x = Symbol("x")
    >>> exp(I*x).expand()
     I*x
    e
    >>> exp(I*x).expand(complex=True)
       -im(x)               -im(x)
    I*e      *sin(re(x)) + e      *cos(re(x))
    >>> x = Symbol("x", real=True)
    >>> exp(I*x).expand(complex=True)
    I*sin(x) + cos(x)

Functions
---------

**trigonometric**::

    >>> sin(x+y).expand(trig=True)
    sin(x)*cos(y) + sin(y)*cos(x)

    >>> cos(x+y).expand(trig=True)
    -sin(x)*sin(y) + cos(x)*cos(y)

    >>> sin(I*x)
    I*sinh(x)

    >>> sinh(I*x)
    I*sin(x)

    >>> asinh(I)
    I*pi
    ----
     2

    >>> asinh(I*x)
    I*asin(x)

    >>> sin(x).series(x, 0, 10)
         3     5     7       9
        x     x     x       x
    x - -- + --- - ---- + ------ + O(x**10)
        6    120   5040   362880

    >>> sinh(x).series(x, 0, 10)
         3     5     7       9
        x     x     x       x
    x + -- + --- + ---- + ------ + O(x**10)
        6    120   5040   362880

    >>> asin(x).series(x, 0, 10)
         3      5      7       9
        x    3*x    5*x    35*x
    x + -- + ---- + ---- + ----- + O(x**10)
        6     40    112     1152

    >>> asinh(x).series(x, 0, 10)
         3      5      7       9
        x    3*x    5*x    35*x
    x - -- + ---- - ---- + ----- + O(x**10)
        6     40    112     1152


**spherical harmonics**::

    >>> from sympy.abc import theta, phi

    >>> Ylm(1, 0, theta, phi)
      ___
    \/ 3 *cos(theta)
    ----------------
            ____
        2*\/ pi

    >>> Ylm(1, 1, theta, phi)
       ___  I*phi
    -\/ 6 *e     *sin(theta)
    ------------------------
                ____
            4*\/ pi

    >>> Ylm(2, 1, theta, phi)
       ____  I*phi
    -\/ 30 *e     *sin(theta)*cos(theta)
    ------------------------------------
                      ____
                  4*\/ pi

**factorials and gamma function**::

    >>> x = Symbol("x")

    >>> y = Symbol("y", integer=True)

    >>> factorial(x)
    x!

    >>> factorial(y)
    y!

    >>> gamma(x + 1).series(x, 0, 3) # i.e. factorial(x)
                         2  2             2  2
                       pi *x    EulerGamma *x
    1 - EulerGamma*x + ------ + -------------- + O(x**3)
                         12           2

**zeta function**::

    >>> zeta(4, x)
    zeta(4, x)

    >>> zeta(4, 1)
      4
    pi
    ---
     90

    >>> zeta(4, 2)
           4
         pi
    -1 + ---
          90

    >>> zeta(4, 3)
             4
      17   pi
    - -- + ---
      16    90


**polynomials**::

    >>> chebyshevt(2, x)
       2
    2*x  - 1

    >>> chebyshevt(4, x)
       4      2
    8*x  - 8*x  + 1

    >>> legendre(2, x)
       2
    3*x    1
    ---- - -
     2     2

    >>> legendre(8, x)
          8         6         4        2
    6435*x    3003*x    3465*x    315*x     35
    ------- - ------- + ------- - ------ + ---
      128        32        64       32     128

    >>> assoc_legendre(2, 1, x)
            __________
           /    2
    -3*x*\/  - x  + 1

    >>> assoc_legendre(2, 2, x)
         2
    - 3*x  + 3

    >>> hermite(3, x)
       3
    8*x  - 12*x

.. index:: equations; differential, diff, dsolve

Differential Equations
----------------------

In ``isympy``::

    >>> f(x).diff(x, x) + f(x)
              2
             d
    f(x) + -----(f(x))
           dx dx

    >>> dsolve(f(x).diff(x, x) + f(x), f(x))
    f(x) = C1*cos(x) + C2*sin(x)


.. index:: equations; algebraic, solve

Algebraic equations
-------------------

In ``isympy``::

    >>> solve(x**4 - 1, x)
    [1, -1, -I, I]

    >>> solve([x + 5*y - 2, -3*x + 6*y - 15], [x, y])
    {x: -3, y: 1}


.. index:: linear algebra

Linear Algebra
==============

.. index:: Matrix

Matrices
--------

Matrices are created as instances from the Matrix class::

    >>> from sympy import Matrix
    >>> Matrix([[1,0], [0,1]])
    [1  0]
    [    ]
    [0  1]

you can also put Symbols in it::

    >>> x = Symbol('x')
    >>> y = Symbol('y')
    >>> A = Matrix([[1,x], [y,1]])
    >>> A
    [1  x]
    [    ]
    [y  1]

    >>> A**2
    [x*y + 1    2*x  ]
    [                ]
    [  2*y    x*y + 1]

For more information an examples with Matrices, see the LinearAlgebraTutorial.

.. index:: pattern matching, match, Wild, WildFunction

Pattern matching
================

Use the ``.match()`` method, along with the ``Wild`` class, to perform pattern
matching on expressions. The method will return a dictionary with the required
substitutions, as follows::

    >>> from sympy import *
    >>> x = Symbol('x')
    >>> p = Wild('p')
    >>> (5*x**2).match(p*x**2)
    {p: 5}

    >>> q = Wild('q')
    >>> (x**2).match(p*x**q)
    {p: 1, q: 2}

If the match is unsuccessful, it returns ``None``::

    >>> print (x+1).match(p**x)
    None

One can also use the exclude parameter of the ``Wild`` class to ensure that
certain things do not show up in the result::

    >>> x = Symbol('x')
    >>> p = Wild('p', exclude=[1,x])
    >>> print (x+1).match(x+p) # 1 is excluded
    None
    >>> print (x+1).match(p+1) # x is excluded
    None
    >>> print (x+1).match(x+2+p) # -1 is not excluded
    {p_: -1}

.. _printing-tutorial:

Printing
========

There are many ways how expressions can be printed.

**Standard**

This is what ``str(expression)`` returns and it looks like this:

    >>> from sympy import Integral
    >>> from sympy.abc import x
    >>> print x**2
    x**2
    >>> print 1/x
    1/x
    >>> print Integral(x**2, x)
    Integral(x**2, x)
    >>>


**Pretty printing**

This is a nice ascii-art printing produced by a ``pprint`` function:

    >>> sys.displayhook = oldhook
    >>> from sympy import Integral, pprint
    >>> from sympy.abc import x
    >>> pprint(x**2)
     2
    x
    >>> pprint(1/x)
    1
    -
    x
    >>> pprint(Integral(x**2, x))
      /
     |
     |  2
     | x  dx
     |
    /

If you have a unicode font installed, it should use unicode pretty printing by default.  You can override this using the `use_unicode` option.:

    >>> pprint(Integral(x**2, x), use_unicode=True)
    ⌠
    ⎮  2
    ⎮ x  dx
    ⌡


See also the wiki `Pretty Printing
<https://github.com/sympy/sympy/wiki/Pretty-Printing>`_ for more examples of a nice
unicode printing.

Tip: To make the pretty printing default in the python interpreter, use::

    $ python
    Python 2.5.2 (r252:60911, Jun 25 2008, 17:58:32)
    [GCC 4.3.1] on linux2
    Type "help", "copyright", "credits" or "license" for more information.
    >>> from sympy import *
    >>> import sys
    >>> sys.displayhook = pprint
    >>> var("x")
    x
    >>> x**3/3
     3
    x
    --
    3
    >>> Integral(x**2, x) #doctest: +NORMALIZE_WHITESPACE
      /
     |
     |  2
     | x  dx
     |
    /

**Python printing**

    >>> from sympy.printing.python import python
    >>> from sympy import Integral
    >>> from sympy.abc import x
    >>> print python(x**2)
    x = Symbol('x')
    e = x**2
    >>> print python(1/x)
    x = Symbol('x')
    e = 1/x
    >>> print python(Integral(x**2, x))
    x = Symbol('x')
    e = Integral(x**2, x)


**LaTeX printing**

    >>> from sympy import Integral, latex
    >>> from sympy.abc import x
    >>> latex(x**2)
    x^{2}
    >>> latex(x**2, mode='inline')
    $x^{2}$
    >>> latex(x**2, mode='equation')
    \begin{equation}x^{2}\end{equation}
    >>> latex(x**2, mode='equation*')
    \begin{equation*}x^{2}\end{equation*}
    >>> latex(1/x)
    \frac{1}{x}
    >>> latex(Integral(x**2, x))
    \int x^{2}\,dx
    >>>

**MathML**

::

    >>> from sympy.printing.mathml import mathml
    >>> from sympy import Integral, latex
    >>> from sympy.abc import x
    >>> print mathml(x**2)
    <apply><power/><ci>x</ci><cn>2</cn></apply>
    >>> print mathml(1/x)
    <apply><power/><ci>x</ci><cn>-1</cn></apply>

**Pyglet**

    >>> from sympy import Integral, preview
    >>> from sympy.abc import x
    >>> preview(Integral(x**2, x)) #doctest:+SKIP

And a pyglet window with the LaTeX rendered expression will popup:

.. image:: pics/pngview1.png

Notes
-----

``isympy`` calls ``pprint`` automatically, so that's why you see pretty
printing by default.

Note that there is also a printing module available, ``sympy.printing``.  Other
printing methods available trough this module are:

* ``pretty(expr)``, ``pretty_print(expr)``, ``pprint(expr)``: Return or print, respectively, a pretty representation of ``expr``. This is the same as the second level of representation described above.

* ``latex(expr)``, ``print_latex(expr)``: Return or print, respectively, a `LaTeX <http://www.latex-project.org/>`_  representation of ``expr``

* ``mathml(expr)``, ``print_mathml(expr)``: Return or print, respectively, a `MathML <http://www.w3.org/Math/>`_ representation of ``expr``.

* ``print_gtk(expr)``: Print ``expr`` to `Gtkmathview <http://helm.cs.unibo.it/mml-widget/>`_, a GTK widget that displays MathML code. The `Gtkmathview <http://helm.cs.unibo.it/mml-widget/>`_ program is required.

Further documentation
=====================

Now it's time to learn more about SymPy. Go through the
:ref:`SymPy User's Guide <guide>` and
:ref:`SymPy Modules Reference <module-docs>`.

Be sure to also browse our public `wiki.sympy.org <http://wiki.sympy.org/>`_,
that contains a lot of useful examples, tutorials, cookbooks that we and our
users contributed and we encourage you to edit it.