### 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 (tQ*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]]`