Characteristic Polynomial of A Product of Two Matrices
If A and B are two square n×n matrices then characteristic polynomials of AB and BA coincide:
More generally, if A is m×n-matrix and B is n×m matrices such that m<n, then AB is m×m and BA is n×n matrix. One has
To prove the first result, recognize that the equation to be proved, as a polynomial in t and in the entries of A and B is a universal polynomial identity. It therefore suffices to check it on an open set of parameter values in the complex numbers. The tuples (A,B,t) where A is an invertible complex n by n matrix, B is any complex n by n matrix, and t is any complex number from an open set in complex space of dimension 2n2 + 1. When A is non-singular our result follows from the fact that AB and BA are similar:
Read more about this topic: Characteristic Polynomial
Famous quotes containing the word product:
“The product of the artist has become less important than the fact of the artist. We wish to absorb this person. We wish to devour someone who has experienced the tragic. In our society this person is much more important than anything he might create.”
—David Mamet (b. 1947)