Comparing the above implementation with the one on the official repo, we’ve identified a few differences. Most of them are minor and they are related to how we initialize the weights (for example Normal initialization vs Truncated Normal), how we parameterize the LR Scheduling (for example smaller vs larger warmup rate, shorter vs longer training) etc. The biggest known difference lies in the way we compute the Classification loss. More specifically the implementation of SSDlite with MobileNetV3 backbone on the official repo doesn’t use the SSD’s Multibox loss but instead uses RetinaNet’s focal loss. This is a rather significant deviation from the paper and since TorchVision already offers a full implementation of RetinaNet, we decided to implement SSDlite using the normal Multi-box SSD loss.