Question about qr shift

I was asked to use qr shift to calculate the eigenvalues of a matrix where the matrix with tolerance 10^(-16). Is qr shift a statement in matlab, please? I only looked up qr or shift. If qr shift does exist how should I use it?

[Christine Tobler]

The algorithm used inside of EIG is called the QR algorithm, and it uses shifts. The tolerance really depends on what error you're talking about, but EIG doesn't provide any tolerance inputs because it computes the result as accurate as is reasonably possible with round-off error.