- Source: Anticommutative property
In mathematics, anticommutativity is a specific property of some non-commutative mathematical operations. Swapping the position of two arguments of an antisymmetric operation yields a result which is the inverse of the result with unswapped arguments. The notion inverse refers to a group structure on the operation's codomain, possibly with another operation. Subtraction is an anticommutative operation because commuting the operands of a − b gives b − a = −(a − b); for example, 2 − 10 = −(10 − 2) = −8. Another prominent example of an anticommutative operation is the Lie bracket.
In mathematical physics, where symmetry is of central importance, or even just in multilinear algebra these operations are mostly (multilinear with respect to some vector structures and then) called antisymmetric operations, and when they are not already of arity greater than two, extended in an associative setting to cover more than two arguments.
Definition
If
A
,
B
{\displaystyle A,B}
are two abelian groups, a bilinear map
f
:
A
2
→
B
{\displaystyle f\colon A^{2}\to B}
is anticommutative if for all
x
,
y
∈
A
{\displaystyle x,y\in A}
we have
f
(
x
,
y
)
=
−
f
(
y
,
x
)
.
{\displaystyle f(x,y)=-f(y,x).}
More generally, a multilinear map
g
:
A
n
→
B
{\displaystyle g:A^{n}\to B}
is anticommutative if for all
x
1
,
…
x
n
∈
A
{\displaystyle x_{1},\dots x_{n}\in A}
we have
g
(
x
1
,
x
2
,
…
x
n
)
=
sgn
(
σ
)
g
(
x
σ
(
1
)
,
x
σ
(
2
)
,
…
x
σ
(
n
)
)
{\displaystyle g(x_{1},x_{2},\dots x_{n})={\text{sgn}}(\sigma )g(x_{\sigma (1)},x_{\sigma (2)},\dots x_{\sigma (n)})}
where
sgn
(
σ
)
{\displaystyle {\text{sgn}}(\sigma )}
is the sign of the permutation
σ
{\displaystyle \sigma }
.
Properties
If the abelian group
B
{\displaystyle B}
has no 2-torsion, implying that if
x
=
−
x
{\displaystyle x=-x}
then
x
=
0
{\displaystyle x=0}
, then any anticommutative bilinear map
f
:
A
2
→
B
{\displaystyle f\colon A^{2}\to B}
satisfies
f
(
x
,
x
)
=
0.
{\displaystyle f(x,x)=0.}
More generally, by transposing two elements, any anticommutative multilinear map
g
:
A
n
→
B
{\displaystyle g\colon A^{n}\to B}
satisfies
g
(
x
1
,
x
2
,
…
x
n
)
=
0
{\displaystyle g(x_{1},x_{2},\dots x_{n})=0}
if any of the
x
i
{\displaystyle x_{i}}
are equal; such a map is said to be alternating. Conversely, using multilinearity, any alternating map is anticommutative. In the binary case this works as follows: if
f
:
A
2
→
B
{\displaystyle f\colon A^{2}\to B}
is alternating then by bilinearity we have
f
(
x
+
y
,
x
+
y
)
=
f
(
x
,
x
)
+
f
(
x
,
y
)
+
f
(
y
,
x
)
+
f
(
y
,
y
)
=
f
(
x
,
y
)
+
f
(
y
,
x
)
=
0
{\displaystyle f(x+y,x+y)=f(x,x)+f(x,y)+f(y,x)+f(y,y)=f(x,y)+f(y,x)=0}
and the proof in the multilinear case is the same but in only two of the inputs.
Examples
Examples of anticommutative binary operations include:
Cross product
Lie bracket of a Lie algebra
Lie bracket of a Lie ring
Subtraction
See also
Commutativity
Commutator
Exterior algebra
Graded-commutative ring
Operation (mathematics)
Symmetry in mathematics
Particle statistics (for anticommutativity in physics).
References
Bourbaki, Nicolas (1989), "Chapter III. Tensor algebras, exterior algebras, symmetric algebras", Algebra. Chapters 1–3, Elements of Mathematics (2nd printing ed.), Berlin-Heidelberg-New York City: Springer-Verlag, ISBN 3-540-64243-9, MR 0979982, Zbl 0904.00001.
External links
Gainov, A.T. (2001) [1994], "Anti-commutative algebra", Encyclopedia of Mathematics, EMS Press. Which references the Original Russian work
Weisstein, Eric W. "Anticommutative". MathWorld.
Kata Kunci Pencarian:
- Anticommutative property
- Commutative property
- Alternating algebra
- Non-associative algebra
- Signed area
- Supercommutative algebra
- Seven-dimensional space
- Graded ring
- Lie superalgebra
- Triple product
