The lowered submatrices in Gaussian elimination are Schur enhances. Write an 
matrix 
with nonzero 
aspect 
as
This factorization represents step one of Gaussian elimination.
After 
phases of Gaussian elimination we’ve got computed the next factorization, wherein the blocks are 
:
the place the primary matrix on the left is the product of the elementary transformations that cut back the primary columns to higher triangular type. Equating 
and 
blocks on this equation offers 
and 
. Therefore 
, which is the Schur complement of 
in .
The following step of the elimination, which zeros out the primary column of 
under the diagonal, succeeds so long as the 
) aspect of is nonzero (or if the entire first column of is zero, wherein case there’s nothing to do, and is singular on this case).
For numerous matrix buildings, comparable to
- Hermitian (or actual symmetric) constructive particular matrices,
- completely constructive matrices,
- matrices diagonally dominant by rows or columns,
-matrices,
one can present that the Schur complement inherits the construction. For these 4 buildings the aspect of the matrix is nonzero, so the success of Gaussian elimination (or equivalently, the existence of an LU factorization) is assured. Within the first three circumstances the preservation of construction can also be the idea for a proof of the numerical stability of Gaussian elimination.
