determinant as a multilinear mapping
Let be an matrix with entries in a field. The matrix is really the same thing as a list of columnvectors of size . Consequently, the determinant
operation
may beregarded as a mapping
The determinant of a matrix is then defined to bewhere denotes the column of .
Starting with the definition
(1) |
the following properties are easily established:
- 1.
the determinant is multilinear;
- 2.
the determinant is anti-symmetric;
- 3.
the determinant of the identity matrix
is .
These three properties uniquely characterize the determinant, andindeed can — some would say should — be used as the definition ofthe determinant operation.
Let us prove this. We proceed by representing elements of as linear combinations of
the standard basis of . Let be an matrix.The column is represented as ; whenceusing multilinearity
The anti-symmetry assumption implies that the expressions vanish if any two of theindices coincide. If all indices are distinct,
the sign in the above expression beingdetermined by the number of transpositions required to rearrangethe list into the list . The sign istherefore the parity of the permutation
. Since wealso assume that
we now recover the original definition(1).