Add retinanet_r50_2x (#7277)

* remove duplicate backbone variant, test=document_fix

* add retinanet_r50_2x

configs/retinanet/README.md

@@ -5,6 +5,7 @@
 | Backbone     | Model     | imgs/GPU | lr schedule | FPS | Box AP | download   | config      |
 | ------------ | --------- | -------- | ----------- | --- | ------ | ---------- | ----------- |
 | ResNet50-FPN | RetinaNet | 2        | 1x          | --- | 37.5   | [model](https://bj.bcebos.com/v1/paddledet/models/retinanet_r50_fpn_1x_coco.pdparams) | [config](./retinanet_r50_fpn_1x_coco.yml) |
+| ResNet50-FPN | RetinaNet | 2        | 2x          | --- | 39.1   | [model](https://bj.bcebos.com/v1/paddledet/models/retinanet_r50_fpn_2x_coco.pdparams) | [config](./retinanet_r50_fpn_2x_coco.yml) |
 | ResNet101-FPN| RetinaNet | 2        | 2x          | --- | 40.6   | [model](https://paddledet.bj.bcebos.com/models/retinanet_r101_fpn_2x_coco.pdparams) | [config](./retinanet_r101_fpn_2x_coco.yml)  |
 | ResNet50-FPN | RetinaNet + [FGD](../slim/distill/README.md) | 2        | 2x          | --- | 40.8    | [model](https://bj.bcebos.com/v1/paddledet/models/retinanet_r101_distill_r50_2x_coco.pdparams) | [config](./retinanet_r50_fpn_2x_coco.yml)/[slim_config](../slim/distill/retinanet_resnet101_coco_distill.yml) |
 

configs/retinanet/_base_/retinanet_r101_fpn.yml

-architecture: RetinaNet
-pretrain_weights:  https://paddledet.bj.bcebos.com/models/pretrained/ResNet101_pretrained.pdparams
-
-RetinaNet:
-  backbone: ResNet
-  neck: FPN
-  head: RetinaHead
-
-ResNet:
-  depth: 101
-  variant: b
-  norm_type: bn
-  freeze_at: 0
-  return_idx: [1,2,3]
-  num_stages: 4
-
-FPN:
-  out_channel: 256
-  spatial_scales: [0.125, 0.0625, 0.03125]
-  extra_stage: 2
-  has_extra_convs: true
-  use_c5: false
-
-RetinaHead:
-  conv_feat:
-    name: RetinaFeat
-    feat_in: 256
-    feat_out: 256
-    num_convs: 4
-    norm_type: null
-    use_dcn: false
-  anchor_generator:
-    name: RetinaAnchorGenerator
-    octave_base_scale: 4
-    scales_per_octave: 3
-    aspect_ratios: [0.5, 1.0, 2.0]
-    strides: [8.0, 16.0, 32.0, 64.0, 128.0]
-  bbox_assigner:
-    name: MaxIoUAssigner
-    positive_overlap: 0.5
-    negative_overlap: 0.4
-    allow_low_quality: true
-  loss_class:
-    name: FocalLoss
-    gamma: 2.0
-    alpha: 0.25
-    loss_weight: 1.0
-  loss_bbox:
-    name: SmoothL1Loss
-    beta: 0.0
-    loss_weight: 1.0
-  nms:
-    name: MultiClassNMS
-    nms_top_k: 1000
-    keep_top_k: 100
-    score_threshold: 0.05
-    nms_threshold: 0.5

configs/retinanet/retinanet_r101_fpn_2x_coco.yml

 _BASE_: [
   '../datasets/coco_detection.yml',
   '../runtime.yml',
-  '_base_/retinanet_r101_fpn.yml',
+  '_base_/retinanet_r50_fpn.yml',
   '_base_/optimizer_2x.yml',
   '_base_/retinanet_reader.yml'
 ]
 
-weights: https://paddledet.bj.bcebos.com/models/retinanet_r101_fpn_2x_coco.pdparams
+weights: output/retinanet_r101_fpn_2x_coco/model_final
+pretrain_weights: https://paddledet.bj.bcebos.com/models/pretrained/ResNet101_pretrained.pdparams
+
+ResNet:
+  depth: 101
+  variant: b
+  norm_type: bn
+  freeze_at: 0
+  return_idx: [1, 2, 3]
+  num_stages: 4

configs/retinanet/retinanet_r50_fpn_2x_coco.yml

+_BASE_: [
+  '../datasets/coco_detection.yml',
+  '../runtime.yml',
+  '_base_/retinanet_r50_fpn.yml',
+  '_base_/optimizer_2x.yml',
+  '_base_/retinanet_reader.yml'
+]
+
+weights: output/retinanet_r50_fpn_2x_coco/model_final