List with two matrices Q and R, Q orthonormal and
R upper triangular, such that A=Q%*%R.

Details

givens(A) returns a QR decomposition (or factorization) of the
square matrix A by applying unitary 2-by-2 matrices U such
that U * [xk;xl] = [x,0] where x=sqrt(xk^2+xl^2)

References

Golub, G. H., and Ch. F. van Loan (1996). Matrix Computations.
Third edition, John Hopkins University Press, Baltimore.