Characteristic polynomial: Identity permutation? This concerns the characteristic polynomial of a matrix.
http://www.math.umn.edu/~olver/num_/lnv.pdf p. 7 (or p. 92).


every term is prescribed by a permutation π
  of the rows of the
  matrix



identity permutation is obtained by multiplying the diagonal entries together


What is the identity permutation?

I do not know much about eigenvalues or characteristic polynomials of   matrices, but the identity permutation is the permutation that keeps the order of everything the same. It's called the identity because that's the naming convention things that keep everything the same. For example, $0$ is the identity of addition and $1$ is the identity of multiplication.
Here's some examples of the identity permutation (I'm going to call the identity permutation here $\sigma$):
$$\sigma(123)=(123)$$
$$(12)\sigma(34)=(12)(34)$$
