Determinant identities
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It has been suggested that this article be merged into determinant. (Discuss) Proposed since April 2018.

In mathematics the determinant is an operator which has certain useful identities.
Identities
where I_{n} is the n × n identity matrix.
provided exists.
For square matrices A and B of equal size,
for an n × n matrix.
If A is a triangular matrix, i.e. a_{i,j} = 0 whenever i > j or, alternatively, whenever i < j, then its determinant equals the product of the diagonal entries:
Schur complement
The following identity holds for a Schur complement of a square matrix:
The Schur complement arises as the result of performing a block Gaussian elimination by multiplying the matrix M from the right with the "block lower triangular" matrix
Here I_{p} denotes a p×p identity matrix. After multiplication with the matrix L the Schur complement appears in the upper p×p block. The product matrix is
That is, we have effected a Gaussian decomposition
The first and last matrices on the RHS have determinant unity, so we have
This is Schur's determinant identity.