Spectrum of a matrix

In mathematics, the spectrum of a (finite-dimensional) matrix is the set of its eigenvalues. This notion can be extended to the spectrum of an operator in the infinite-dimensional case.

The determinant equals the product of the eigenvalues. Similarly, the trace equals the sum of the eigenvalues. From this point of view, we can define the Pseudo-determinant for a singular matrix to be the product of all the nonzero eigenvalues (the density of Multivariate normal distribution will need this quantity).