This is an unofficial implementation of Focal Loss (https://arxiv.org/abs/1708.02002).
A python layer for focal loss is added, and a couple of files are modified from the original mxnet ssd example (https://github.com/apache/incubator-mxnet/tree/master/example/ssd).
Put focal_loss_layer.py into ssd/tools and copy other files to their respective directories (don't forget to backup files before overwriting).