Global minimum Chapter4. Page(119)

Hi @ageron,

1. so in chapter 2 we used the sklearn Linear regressor model and calculated the RMSE. In chapter 4 we learn about normal equation and Gradient descent which help us optimize the cost function. My question is if I were using the Linear Regressor as a black box. How would I know the RMSE I have is the global minimum.? Like how would I appreciate how good the model worked from looking at the RMSE.
2. In chapter 4 you talk about using Gridsearch to find the appropriate learning rate. I picture Gridesearch as using it on an algorithm with tunable hyperparameters. So how will I do this because the Linear Regressor alg for example has no learning rate hyperparameter.
could you please just show like a code which does the gridsearch and assigns a stop tolearnce.
Thanks :)