【PPSCI Doc No.38-40】 (#826)

* ppsci.equation.PDE.parameters/state_dict/set_state_dict api fix

* ppsci.equation.PDE.parameters/state_dict/set_state_dict api fix

---------

Co-authored-by: krp <2934631798@qq.com>

ppsci/equation/pde/base.py

@@ -83,19 +83,71 @@ def add_equation(self, name: str, equation: Callable):
         self.equations.update({name: equation})
 
     def parameters(self) -> List[paddle.Tensor]:
-        """Return parameters contained in PDE.
+        """Return learnable parameters contained in PDE.
+
+        Args:
+            None
 
         Returns:
-            List[Tensor]: A list of parameters.
+            List[Tensor]: A list of learnable parameters.
+
+        Examples:
+            >>> import ppsci
+            >>> pde = ppsci.equation.Vibration(2, -4, 0)
+            >>> print(pde.parameters())
+            [Parameter containing:
+            Tensor(shape=[], dtype=float32, place=Place(gpu:0), stop_gradient=False,
+                   -4.), Parameter containing:
+            Tensor(shape=[], dtype=float32, place=Place(gpu:0), stop_gradient=False,
+                   0.)]
         """
         return self.learnable_parameters.parameters()
 
     def state_dict(self) -> Dict[str, paddle.Tensor]:
-        """Return named parameters in dict."""
+        """Return named learnable parameters in dict.
+
+        Args:
+            None
+
+        Returns:
+            Dict[str, Tensor]: A dict of states(str) and learnable parameters(Tensor).
+
+        Examples:
+            >>> import ppsci
+            >>> pde = ppsci.equation.Vibration(2, -4, 0)
+            >>> print(pde.state_dict())
+            OrderedDict([('0', Parameter containing:
+            Tensor(shape=[], dtype=float64, place=Place(gpu:0), stop_gradient=False,
+                   -4.)), ('1', Parameter containing:
+            Tensor(shape=[], dtype=float64, place=Place(gpu:0), stop_gradient=False,
+                   0.))])
+        """
+
         return self.learnable_parameters.state_dict()
 
-    def set_state_dict(self, state_dict):
-        """Set state dict from dict."""
+    def set_state_dict(self, state_dict: Dict[str, paddle.Tensor]):
+        """Set state dict from dict.
+
+        Args:
+            state_dict (Dict[str, paddle.Tensor]): The state dict to be set.
+
+        Returns:
+            None
+
+        Examples:
+            >>> import paddle
+            >>> import ppsci
+            >>> paddle.set_default_dtype("float64")
+            >>> pde = ppsci.equation.Vibration(2, -4, 0)
+            >>> state = pde.state_dict()
+            >>> state['0'] = paddle.to_tensor(-3.1)
+            >>> pde.set_state_dict(state)
+            >>> print(state)
+            OrderedDict([('0', Tensor(shape=[], dtype=float64, place=Place(gpu:0), stop_gradient=True,
+                   -3.10000000)), ('1', Parameter containing:
+            Tensor(shape=[], dtype=float64, place=Place(gpu:0), stop_gradient=False,
+                   0.))])
+        """
         self.learnable_parameters.set_state_dict(state_dict)
 
     def __str__(self):