Generalized functions

Sage implements several generalized functions (also known as distributions) such as Dirac delta, Heaviside step functions. These generalized functions can be manipulated within Sage like any other symbolic functions.

AUTHORS:

• Golam Mortuza Hossain (2009-06-26): initial version

EXAMPLES:

Dirac delta function:

sage: dirac_delta(x)                                                                # needs sage.symbolic
dirac_delta(x)

Heaviside step function:

sage: heaviside(x)                                                                  # needs sage.symbolic
heaviside(x)

Unit step function:

sage: unit_step(x)                                                                  # needs sage.symbolic
unit_step(x)

Signum (sgn) function:

sage: sgn(x)                                                                        # needs sage.symbolic
sgn(x)

Kronecker delta function:

sage: m, n = var('m,n')                                                             # needs sage.symbolic
sage: kronecker_delta(m, n)                                                         # needs sage.symbolic
kronecker_delta(m, n)

class sage.functions.generalized.FunctionDiracDelta

Bases: BuiltinFunction

The Dirac delta (generalized) function, $\delta (x)$ (dirac_delta(x)).

INPUT:

• x – a real number or a symbolic expression

DEFINITION:

Dirac delta function $\delta (x)$, is defined in Sage as:

$\delta (x)=0$ for real $x\ne 0$ and ${\int }_{-\mathrm{\infty }}^{\mathrm{\infty }}\delta (x)dx=1$

Its alternate definition with respect to an arbitrary test function $f(x)$ is

${\int }_{-\mathrm{\infty }}^{\mathrm{\infty }}f(x)\delta (x-a)dx=f(a)$

EXAMPLES:

sage: # needs sage.symbolic
sage: dirac_delta(1)
0
sage: dirac_delta(0)
dirac_delta(0)
sage: dirac_delta(x)
dirac_delta(x)
sage: integrate(dirac_delta(x), x, -1, 1, algorithm='sympy')                    # needs sympy
1

REFERENCES:

• Wikipedia article Dirac_delta_function

class sage.functions.generalized.FunctionHeaviside

Bases: GinacFunction

The Heaviside step function, $H(x)$ (heaviside(x)).

INPUT:

• x – a real number or a symbolic expression

DEFINITION:

The Heaviside step function, $H(x)$ is defined in Sage as:

$H(x)=0$ for $x<0$ and $H(x)=1$ for $x>0$

See also

unit_step()

EXAMPLES:

sage: # needs sage.symbolic
sage: heaviside(-1)
0
sage: heaviside(1)
1
sage: heaviside(0)
heaviside(0)
sage: heaviside(x)
heaviside(x)

sage: heaviside(-1/2)                                                           # needs sage.symbolic
0
sage: heaviside(exp(-1000000000000000000000))                                   # needs sage.symbolic
1

REFERENCES:

• Wikipedia article Heaviside_function

class sage.functions.generalized.FunctionKroneckerDelta

Bases: BuiltinFunction

The Kronecker delta function ${\delta }_{m,n}$ (kronecker_delta(m, n)).

INPUT:

• m – a number or a symbolic expression

• n – a number or a symbolic expression

DEFINITION:

Kronecker delta function ${\delta }_{m,n}$ is defined as:

${\delta }_{m,n}=0$ for $m\ne n$ and ${\delta }_{m,n}=1$ for $m=n$

EXAMPLES:

sage: kronecker_delta(1, 2)                                                     # needs sage.rings.complex_interval_field
0
sage: kronecker_delta(1, 1)                                                     # needs sage.rings.complex_interval_field
1
sage: m, n = var('m,n')                                                         # needs sage.symbolic
sage: kronecker_delta(m, n)                                                     # needs sage.symbolic
kronecker_delta(m, n)

REFERENCES:

• Wikipedia article Kronecker_delta

class sage.functions.generalized.FunctionSignum

Bases: BuiltinFunction

The signum or sgn function $\mathrm{sgn}(x)$ (sgn(x)).

INPUT:

• x – a real number or a symbolic expression

DEFINITION:

The sgn function, $\mathrm{sgn}(x)$ is defined as:

$\mathrm{sgn}(x)=1$ for $x>0$, $\mathrm{sgn}(x)=0$ for $x=0$ and $\mathrm{sgn}(x)=-1$ for $x<0$

EXAMPLES:

sage: sgn(-1)
-1
sage: sgn(1)
1
sage: sgn(0)
0
sage: sgn(x)                                                                    # needs sage.symbolic
sgn(x)

We can also use sign:

sage: sign(1)
1
sage: sign(0)
0
sage: a = AA(-5).nth_root(7)                                                    # needs sage.rings.number_field
sage: sign(a)                                                                   # needs sage.rings.number_field
-1

REFERENCES:

• Wikipedia article Sign_function

class sage.functions.generalized.FunctionUnitStep

Bases: GinacFunction

The unit step function, $\mathrm{u}(x)$ (unit_step(x)).

INPUT:

• x – a real number or a symbolic expression

DEFINITION:

The unit step function, $\mathrm{u}(x)$ is defined in Sage as:

$\mathrm{u}(x)=0$ for $x<0$ and $\mathrm{u}(x)=1$ for $x\ge 0$

See also

heaviside()

EXAMPLES:

sage: # needs sage.symbolic
sage: unit_step(-1)
0
sage: unit_step(1)
1
sage: unit_step(0)
1
sage: unit_step(x)
unit_step(x)
sage: unit_step(-exp(-10000000000000000000))
0