clear differentiation cache in visu_forward to avoid OOM problem (#757)

Author: HydrogenSulfate

examples/bubble/bubble.py

@@ -362,7 +362,7 @@ def transform_out(in_, out):
         NPOINT_PDE * NTIME_PDE, evenly=True
     )
 
-    pred_norm = solver.predict(visu_mat, no_grad=False, return_numpy=True)
+    pred_norm = solver.predict(visu_mat, None, 4096, no_grad=False, return_numpy=True)
     # inverse normalization
     p_pred = pred_norm["p"].reshape([NTIME_PDE, NPOINT_PDE]).T
     u_pred = pred_norm["u"].reshape([NTIME_PDE, NPOINT_PDE]).T

ppsci/utils/expression.py

@@ -185,7 +185,7 @@ def visu_forward(
             for name, expr in expr_dict.items():
                 output_dict[name] = expr(data_dict)
 
-            # clear differentiation cache
-            clear()
+        # clear differentiation cache
+        clear()
 
         return output_dict