add the examples for the mm (#38669)

* add the examples for the mm

* fix the document of paddle.mm

python/paddle/tensor/math.py

@@ -1118,6 +1118,38 @@ def mm(input, mat2, name=None):
     Returns:
         Tensor: The product Tensor.
 
+    ::
+
+        * example 1:
+
+        input: [B, ..., M, K], mat2: [B, ..., K, N]
+        out: [B, ..., M, N]
+
+        * example 2:
+
+        input: [B, M, K], mat2: [B, K, N]
+        out: [B, M, N]
+
+        * example 3:
+
+        input: [B, M, K], mat2: [K, N]
+        out: [B, M, N]
+
+        * example 4:
+
+        input: [M, K], mat2: [K, N]
+        out: [M, N]
+
+        * example 5:
+
+        input: [B, M, K], mat2: [K]
+        out: [B, M]
+
+        * example 6:
+
+        input: [K], mat2: [K]
+        out: [1]
+
     Examples:
         .. code-block:: python