# A calculus of the absurd

##### 20.3.3 QR decomposition

IMPORTANT this section requires knowledge of inner product spaces (see section 20.8).

An LU decomposition splits a matrix into two matrices multiplied together - a lower triangular and an upper triangular matrix. A QR-decomposition also splits a matrix into two parts - an orthogonal matrix, and a right-upper triangular matrix (the letters make a little less sense here).