[Doc] Update docstring of pow()

python/taichi/lang/ops.py

@@ -732,10 +732,18 @@ def expr_python_mod(a, b):
 def pow(x, a):  # pylint: disable=W0622
     """First array elements raised to powers from second array :math:`x^a`, element-wise.
 
-    Negative values raised to a non-integral value will return `nan`.
-    A zero value raised to a negative value will return `inf`.
-    If debug mode or optimization passes are on, an exception will be raised
-    when an integral value is raised to a negative value; otherwise 1 will be returned.
+    The result type of two scalar operands is determined as follows:
+    - If the exponent is an integral value, then the result type takes the type of the base.
+    - Otherwise, the result type follows
+      [Implicit type casting in binary operations](https://docs.taichi-lang.org/docs/type#implicit-type-casting-in-binary-operations).
+
+    With the above rules, an integral value raised to a negative integral value cannot have a
+    feasible type. Therefore, an exception will be raised if debug mode or optimization passes
+    are on; otherwise 1 will be returned.
+
+    In the following situations, the result is undefined:
+    - A negative value raised to a non-integral value.
+    - A zero value raised to a non-positive value.
 
     Args:
         x (Union[:mod:`~taichi.types.primitive_types`, :class:`~taichi.Matrix`]): \
@@ -744,20 +752,20 @@ def pow(x, a):  # pylint: disable=W0622
             The exponents.
 
     Returns:
-        The bases in `x1` raised to the exponents in `x2`. This is a scalar if both \
-            `x1` and `x2` are scalars.
+        The bases in `x` raised to the exponents in `a`. This is a scalar if both \
+            `x` and `a` are scalars.
 
     Example::
 
         >>> @ti.kernel
         >>> def test():
-        >>>     x = ti.Matrix([-2.0, 0.0, 2.0])
-        >>>     y = -2.2
+        >>>     x = ti.Matrix([-2.0, 2.0])
+        >>>     y = -3
         >>>     z = ti.pow(x, y)
         >>>     print(z)
         >>>
         >>> test()
-        [-nan, inf, 0.217638]
+        [-0.125000, 0.125000]
     """
     return _binary_operation(_ti_core.expr_pow, _bt_ops_mod.pow, x, a)