diagonalization

Noun

diagonalisation (countable and uncountable, plural diagonalisations)

1. In matrix algebra, the process of converting a square matrix into a diagonal matrix, usually to find the eigenvalues of the matrix.
2. An argument used in proof by contradiction by constructing a supposedly exhaustive list of all members of a class, and then subsequently constructing a new member which differs from each existing member in at least one place and therefore cannot belong to the list.