### 2.48.2 QR decomposition : `qr`

`qr` takes as argument a numeric
square matrix *A* of size *n*.

`qr` factorizes numerically
this matrix as *Q***R* where
*Q* is an orthogonal matrix (^{t}*Q***Q*=*I*) and *R* is an upper triangular
matrix.
`qr(A)` returns only `R`, run `Q=A*inv(R)` to get `Q`.

Input :

`qr([[3,5],[4,5]])`

Output is the matrix `R` :

`[[-5,-7],[0,-1]]`

Input :

`qr([[1,2],[3,4]])`

Output is the matrix `R` :

`[[-3.16227766017,-4.42718872424],[0,-0.632455532034]] `