# GMRES Matlab 'tol' parameter

I need to use GMRES solver in MATLAB, and I need to play around with the codes parameters and I had a very simple question about its usage.

The documentation of the solver here mentions a parameter tol which they do not seem to have defined except that the defuault value is $10^{-6}$.

What is this number? There don't seem to be any definitions of this anywhere on the web.

Is it the upper-bound on $\frac{||b-Ax_k||}{||b||}$ where we are solving $Ax=b$ and $x_k$ is the current GMRES iterate?

It is indeed a tolerance on the relative residual $$||b-Ax_k|| / ||b||$$