fix expand shape problem (#3745)

ppdet/modeling/necks/yolo_fpn.py

@@ -24,28 +24,23 @@ __all__ = ['YOLOv3FPN', 'PPYOLOFPN', 'PPYOLOTinyFPN', 'PPYOLOPAN']
 
 
 def add_coord(x, data_format):
-    b = x.shape[0]
     if data_format == 'NCHW':
-        h = x.shape[2]
-        w = x.shape[3]
+        b, _, h, w = paddle.shape(x)
     else:
-        h = x.shape[1]
-        w = x.shape[2]
+        b, h, w, _ = paddle.shape(x)
 
-    gx = paddle.arange(w, dtype='float32') / (w - 1.) * 2.0 - 1.
-    if data_format == 'NCHW':
-        gx = gx.reshape([1, 1, 1, w]).expand([b, 1, h, w])
-    else:
-        gx = gx.reshape([1, 1, w, 1]).expand([b, h, w, 1])
-    gx.stop_gradient = True
+    gx = paddle.arange(w, dtype=x.dtype) / ((w - 1.) * 2.0) - 1.
+    gy = paddle.arange(h, dtype=x.dtype) / ((h - 1.) * 2.0) - 1.
 
-    gy = paddle.arange(h, dtype='float32') / (h - 1.) * 2.0 - 1.
     if data_format == 'NCHW':
+        gx = gx.reshape([1, 1, 1, w]).expand([b, 1, h, w])
         gy = gy.reshape([1, 1, h, 1]).expand([b, 1, h, w])
     else:
+        gx = gx.reshape([1, 1, w, 1]).expand([b, h, w, 1])
         gy = gy.reshape([1, h, 1, 1]).expand([b, h, w, 1])
-    gy.stop_gradient = True
 
+    gx.stop_gradient = True
+    gy.stop_gradient = True
     return gx, gy