noun. In matrix algebra, the process of converting a square matrix into a diagonal matrix, usually to find the eigenvalues of the matrix.

noun. changing a square matrix to diagonal form (with all non-zero elements on the principal diagonal)

"Second, the method that is used, called diagonalisation was already present in the work of du Bois-Reymond for building real functions growing faster than any function in a given sequence of functions."

resolution  resolving  

diagonalization