Pexpect Interface to Giac#

(You should prefer the cython interface: giacpy_sage and its libgiac command)

(adapted by F. Han from William Stein and Gregg Musiker maple’s interface)

You must have the Giac interpreter installed and available as the command giac in your PATH in order to use this interface. You need a giac version supporting “giac –sage” ( roughly after 0.9.1 ). In this case you do not have to install any optional Sage packages. If giac is not already installed, you can download binaries or sources or spkg (follow the sources link) from the homepage:

Homepage <https://www-fourier.ujf-grenoble.fr/~parisse/giac.html>

Type giac.[tab] for a list of all the functions available from your Giac install. Type giac.[tab]? for Giac’s help about a given function. Type giac(...) to create a new Giac object, and giac.eval(...) to run a string using Giac (and get the result back as a string).

If the giac spkg is installed, you should find the full html documentation there:

$SAGE_LOCAL/share/giac/doc/en/cascmd_local/index.html

EXAMPLES:

sage: giac('3 * 5')
15
sage: giac.eval('ifactor(2005)')
'5*401'
sage: giac.ifactor(2005)
2005
sage: l=giac.ifactors(2005) ; l; l[2]
[5,1,401,1]
401
sage: giac.fsolve('x^2=cos(x)+4', 'x','0..5')
[1.9140206190...
sage: giac.factor('x^4 - y^4')
(x-y)*(x+y)*(x^2+y^2)
sage: R.<x,y>=QQ[];f=(x+y)^5;f2=giac(f);(f-f2).normal()
0
sage: x,y=giac('x,y'); giac.int(y/(cos(2*x)+cos(x)),x)     # random
y*2*((-(tan(x/2)))/6+(-2*1/6/sqrt(3))*ln(abs(6*tan(x/2)-2*sqrt(3))/abs(6*tan(x/2)+2*sqrt(3))))

If the string “error” (case insensitive) occurs in the output of anything from Giac, a RuntimeError exception is raised.

Tutorial#

AUTHORS:

  • Gregg Musiker (2006-02-02): initial version.

  • Frederic Han: adapted to giac.

  • Marcelo Forets (2017-04-06): conversions and cleanup.

This tutorial is based on the Maple Tutorial for number theory from http://www.math.mun.ca/~drideout/m3370/numtheory.html.

Syntax#

There are several ways to use the Giac Interface in Sage. We will discuss two of those ways in this tutorial.

  1. If you have a giac expression such as

    factor( (x^4-1));

    We can write that in sage as

    sage: giac('factor(x^4-1)')
(x-1)*(x+1)*(x^2+1)

    Notice, there is no need to use a semicolon.

  2. Since Sage is written in Python, we can also import giac commands and write our scripts in a pythonic way. For example, factor() is a giac command, so we can also factor in Sage using

    sage: giac('(x^4-1)').factor()
(x-1)*(x+1)*(x^2+1)

    where expression.command() means the same thing as command(expression) in Giac. We will use this second type of syntax whenever possible, resorting to the first when needed.

    sage: giac('(x^12-1)/(x-1)').normal()
x^11+x^10+x^9+x^8+x^7+x^6+x^5+x^4+x^3+x^2+x+1

Some typical input#

The normal command will reduce a rational function to the lowest terms. In giac, simplify is slower than normal because it tries more sophisticated simplifications (ex algebraic extensions) The factor command will factor a polynomial with rational coefficients into irreducible factors over the ring of integers (if your default configuration of giac (cf .xcasrc) has not allowed square roots). So for example,

sage: giac('(x^12-1)').factor( )
(x-1)*(x+1)*(x^2+1)*(x^2-x+1)*(x^2+x+1)*(x^4-x^2+1)

sage: giac('(x^28-1)').factor( )
(x-1)*(x+1)*(x^2+1)*(x^6-x^5+x^4-x^3+x^2-x+1)*(x^6+x^5+x^4+x^3+x^2+x+1)*(x^12-x^10+x^8-x^6+x^4-x^2+1)

Giac console#

Another important feature of giac is its online help. We can access this through sage as well. After reading the description of the command, you can press q to immediately get back to your original prompt.

Incidentally you can always get into a giac console by the command

sage: giac.console()                       # not tested
sage: !giac                                # not tested

Note that the above two commands are slightly different, and the first is preferred.

For example, for help on the giac command factors, we type

sage: giac.help('factors')                     # not tested

sage: alpha = giac((1+sqrt(5))/2)
sage: beta = giac(1-sqrt(5))/2
sage: f19  = alpha^19 - beta^19/sqrt(5)
sage: f19
(sqrt(5)/2+1/2)^19-((-sqrt(5)+1)/2)^19/sqrt(5)
sage: (f19-(5778*sqrt(5)+33825)/5).normal()
0

Function definitions#

Let’s say we want to write a giac program now that squares a number if it is positive and cubes it if it is negative. In giac, that would look like

mysqcu := proc(x)
if x > 0 then x^2;
else x^3; fi;
end;

In Sage, we write

sage: mysqcu = giac('proc(x) if x > 0 then x^2 else x^3 fi end')
sage: mysqcu(5)
25
sage: mysqcu(-5)
-125

More complicated programs should be put in a separate file and loaded.

Conversions#

The GiacElement.sage() method tries to convert a Giac object to a Sage object. In many cases, it will just work. In particular, it should be able to convert expressions entirely consisting of:

  • numbers, i.e. integers, floats, complex numbers;

  • functions and named constants also present in Sage, where Sage knows how to translate the function or constant’s name from Giac’s

  • symbolic variables whose names don’t pathologically overlap with objects already defined in Sage.

This method will not work when Giac’s output includes functions unknown to Sage.

If you want to convert more complicated Giac expressions, you can instead call GiacElement._sage_() and supply a translation dictionary:

sage: g = giac('NewFn(x)')
sage: g._sage_(locals={('NewFn', 1): sin})
sin(x)

Moreover, new conversions can be permanently added using Pynac’s register_symbol, and this is the recommended approach for library code. For more details, see the documentation for ._sage_().

class sage.interfaces.giac.Giac(maxread=None, script_subdirectory=None, server=None, server_tmpdir=None, logfile=None)#

Bases: Expect

Interface to the Giac interpreter.

You must have the optional Giac interpreter installed and available as the command giac in your PATH in order to use this interface. Try the command: print(giac._install_hints()) for more informations on giac installation.

Type giac.[tab] for a list of all the functions available from your Giac install. Type giac.[tab]? for Giac’s help about a given function. Type giac(...) to create a new Giac object.

Full html documentation for giac is available from your giac installation at $PREFIX/share/giac/doc/en/cascmd_en/index.html

EXAMPLES:

Any Giac instruction can be evaluated as a string by the giac command. You can access the giac functions by adding the giac. prefix to the usual Giac name.

sage: l=giac('normal((y+sqrt(2))^4)'); l
y^4+4*sqrt(2)*y^3+12*y^2+8*sqrt(2)*y+4
sage: f=giac('(u,v)->{ if (u<v){ [u,v] } else { [v,u] }}');f(1,2),f(3,1)
([1,2], [1,3])

The output of the giac command is a Giac object, and it can be used for another giac command.

sage: l.factors()
[y+sqrt(2),4]
sage: giac('(x^12-1)').factor( )
(x-1)*(x+1)*(x^2+1)*(x^2-x+1)*(x^2+x+1)*(x^4-x^2+1)
sage: giac('assume(y>0)'); giac('y^2=3').solve('y')
y
...[sqrt(3)]

You can create some Giac elements and avoid many quotes like this:

sage: x,y,z=giac('x,y,z');type(y)
<class 'sage.interfaces.giac.GiacElement'>
sage: I1=(1/(cos(2*y)+cos(y))).integral(y,0,pi/4).simplify()
sage: (I1-((-2*ln((sqrt(3)-3*tan(1/8*pi))/(sqrt(3)+3*tan(1/8*pi)))*sqrt(3)-3*tan(1/8*pi))/9)).normal()
0
sage: ((y+z*sqrt(5))*(y-sqrt(5)*z)).normal()
y^2-5*z^2

Polynomials or elements of SR can be evaluated directly by the giac interface.

sage: R.<a,b> = QQ[]; f = (2+a+b)
sage: p = giac.gcd(f^3+5*f^5,f^2+f^5); p; R(p.sage())
sageVARa^2+2*sageVARa*sageVARb+4*sageVARa+sageVARb^2+4*sageVARb+4
a^2 + 2*a*b + b^2 + 4*a + 4*b + 4

Variable names in python and giac are independent:

sage: a=sqrt(2);giac('Digits:=30;a:=5');a,giac('a'),giac(a),giac(a).evalf()
30
(sqrt(2), 5, sqrt(2), 1.41421356237309504880168872421)
clear(var)#

Clear the variable named var.

EXAMPLES:

sage: giac.set('xx', '2')
sage: giac.get('xx')
'2'
sage: giac.clear('xx')
sage: giac.get('xx')
'xx'
completions(s)#

Return all commands that complete the command starting with the string s.

EXAMPLES:

sage: c = giac.completions('cas')
sage: 'cas_setup' in c
True
console()#

Spawn a new Giac command-line session.

EXAMPLES:

sage: giac_console()                   # not tested - giac
...
Homepage http://www-fourier.ujf-grenoble.fr/~parisse/giac.html
Released under the GPL license 3.0 or above
See http://www.gnu.org for license details
-------------------------------------------------
Press CTRL and D simultaneously to finish session
Type ?commandname for help
0>>
cputime(t=None)#

Return the amount of CPU time that the Giac session has used.

If t is not None, then it returns the difference between the current CPU time and t.

EXAMPLES:

sage: t = giac.cputime()
sage: t                     # random
0.02
sage: x = giac('x')
sage: giac.diff(x^2, x)
2*x
sage: giac.cputime(t)       # random
0.0
eval(code, strip=True, **kwds)#

Send the code x to the Giac interpreter. Remark: To enable multi-lines codes in the notebook magic mode: %giac, the \n are removed before sending the code to giac.

INPUT:

  • code – str

  • strip – Default is True and removes \n

EXAMPLES:

sage: giac.eval("2+2;\n3")
'4,3'
sage: giac.eval("2+2;\n3",False)
'4\n3'
sage: s='g(x):={\nx+1;\nx+2;\n}'
sage: giac(s)
...x+1...x+2...
sage: giac.g(5)
7
expect()#

Return the pexpect object for this Giac session.

EXAMPLES:

sage: m = Giac()
sage: m.expect() is None
True
sage: m._start()
sage: m.expect()
Giac with PID ... running .../giac --sage
sage: m.quit()
get(var)#

Get the value of the variable var.

EXAMPLES:

sage: giac.set('xx', '2')
sage: giac.get('xx')
'2'
help(string)#

Display Giac help about string.

This is the same as typing “?string” in the Giac console.

INPUT:

  • string – a string to search for in the giac help system

EXAMPLES:

sage: giac.help('Psi')         # not tested - depends of giac and $LANG
Psi(a,n)=nth-derivative of the function DiGamma (=ln@Gamma) at point a (Psi(a,0)=Psi(a))...
set(var, value)#

Set the variable var to the given value.

EXAMPLES:

sage: giac.set('xx', '2')
sage: giac.get('xx')
'2'
version()#

Wrapper for giac’s version().

EXAMPLES:

sage: giac.version()
"giac...
class sage.interfaces.giac.GiacElement(parent, value, is_name=False, name=None)#

Bases: ExpectElement

integral(var='x', min=None, max=None)#

Return the integral of self with respect to the variable x.

INPUT:

  • var - variable

  • min - default: None

  • max - default: None

This returns the definite integral if xmin is not None, otherwise an indefinite integral.

EXAMPLES:

sage: y=giac('y');f=(sin(2*y)/y).integral(y).simplify(); f
Si(2*y)
sage: f.diff(y).simplify()
sin(2*y)/y

sage: f = giac('exp(x^2)').integral('x',0,1) ; f
1.46265174...
sage: x,y=giac('x'),giac('y');integrate(cos(x+y),'x=0..pi').simplify()
-2*sin(y)
integrate(var='x', min=None, max=None)#

Return the integral of self with respect to the variable x.

INPUT:

  • var - variable

  • min - default: None

  • max - default: None

This returns the definite integral if xmin is not None, otherwise an indefinite integral.

EXAMPLES:

sage: y=giac('y');f=(sin(2*y)/y).integral(y).simplify(); f
Si(2*y)
sage: f.diff(y).simplify()
sin(2*y)/y

sage: f = giac('exp(x^2)').integral('x',0,1) ; f
1.46265174...
sage: x,y=giac('x'),giac('y');integrate(cos(x+y),'x=0..pi').simplify()
-2*sin(y)
sum(var, min=None, max=None)#

Return the sum of self with respect to the variable x.

INPUT:

  • var - variable

  • min - default: None

  • max - default: None

This returns the definite integral if xmin is not None, otherwise an indefinite integral.

EXAMPLES:

sage: giac('1/(1+k^2)').sum('k',-oo,+infinity).simplify()
(pi*exp(pi)^2+pi)/(exp(pi)^2-1)
unapply(var)#

Creates a Giac function in the given arguments from a Giac symbol.

EXAMPLES:

sage: f=giac('y^3+1+t')
sage: g=(f.unapply('y,t'))
sage: g
(y,t)->y^3+1+t
sage: g(1,2)
4
class sage.interfaces.giac.GiacFunction(parent, name)#

Bases: ExpectFunction

class sage.interfaces.giac.GiacFunctionElement(obj, name)#

Bases: FunctionElement

sage.interfaces.giac.giac_console()#

Spawn a new Giac command-line session.

EXAMPLES:

sage: giac.console()  # not tested - giac
...
Homepage http://www-fourier.ujf-grenoble.fr/~parisse/giac.html
Released under the GPL license 3.0 or above
See http://www.gnu.org for license details
-------------------------------------------------
Press CTRL and D simultaneously to finish session
Type ?commandname for help
sage.interfaces.giac.reduce_load_Giac()#

Return the giac object created in sage.interfaces.giac.

EXAMPLES:

sage: from sage.interfaces.giac import reduce_load_Giac
sage: reduce_load_Giac()
Giac