refine unittest test=develop

Author: jerrywgz

paddle/fluid/operators/roi_align_op.cc

@@ -132,7 +132,20 @@ class ROIAlignOpMaker : public framework::OpProtoAndCheckerMaker {
                  "and pooled_w, likewise for height")
         .SetDefault(-1);
     AddComment(R"DOC(
-    
+**RoIAlign Operator**
+
+Region of interest align (also known as RoI align) is to perform
+bilinear interpolation on inputs of nonuniform sizes to obtain 
+fixed-size feature maps (e.g. 7*7)
+
+Dividing each region proposal into equal-sized sections with
+the pooled_width and pooled_height. Location remains the origin
+result.
+
+In each ROI bin, the value of the four regularly sampled locations 
+are computed directly through bilinear interpolation. The output is
+the mean of four locations.
+Thus avoid the misaligned problem.   
     )DOC");
   }
 };

python/paddle/fluid/tests/unittests/test_roi_align_op.py

@@ -167,4 +167,4 @@ def test_check_output(self):
         self.check_output()
 
     def test_check_grad(self):
-        self.check_grad(['X'], 'Out', max_relative_error=0.005)
+        self.check_grad(['X'], 'Out')