If I understood well you have 2 questions.
How to get the bounding box given the network output
What Smooth L1 loss is
The answer to your first question lies in the equation (2) in the section 3.2.1 from the Faster R-CNN paper. As all anchor based object detector (Faster RCNN, YOLOv3, EfficientNets, FPN...) the regression output from the network are not ...
Convergence analysis is about proving that your policy and/or value function converge to some desired value, which is usually the fixed-point of an operator or an extremum. So it essentially proves that theoretically the algorithm achieves the desired function. Without convergence, we have no guarantees that the value function will be accurate or the policy ...
A good example is the degree of freedom in Student's distribution:
The degrees of freedom refers to the number of independent observations in a set of data.
When estimating a mean score or a proportion from a single sample, the number of independent observations is equal to the sample size minus one.
e.g, if we have 100 observation $X_1, \...