fix the sign method of affine transformation (#613)

src/gluonts/distribution/bijection.py

@@ -12,7 +12,7 @@
 # permissions and limitations under the License.
 
 # Standard library imports
-from typing import Optional
+from typing import Optional, Union
 
 # Third-party imports
 import numpy as np
@@ -74,7 +74,7 @@ def event_dim(self) -> int:
  raise NotImplementedError()
 
  @property
- def sign(self) -> Tensor:
+ def sign(self) -> Union[float, Tensor]:
  """
  Return the sign of the Jacobian's determinant.
  """
@@ -96,6 +96,7 @@ class InverseBijection(Bijection):
 
  @validated()
  def __init__(self, bijection: Bijection) -> None:
+ super().__init__(self)
  self._bijection = bijection
 
  def f(self, x: Tensor) -> Tensor:
@@ -115,7 +116,7 @@ def event_dim(self) -> int:
  return self._bijection.event_dim
 
  @property
- def sign(self) -> Tensor:
+ def sign(self) -> Union[float, Tensor]:
  return self._bijection.sign
 
 
@@ -134,7 +135,7 @@ def event_dim(self) -> int:
  return 0
 
  @property
- def sign(self) -> Tensor:
+ def sign(self) -> float:
  return 1.0
 
 
@@ -153,7 +154,7 @@ def event_dim(self) -> int:
  return 0
 
  @property
- def sign(self) -> Tensor:
+ def sign(self) -> float:
  return 1.0
 
 
@@ -183,7 +184,7 @@ def event_dim(self) -> int:
  return 0
 
  @property
- def sign(self) -> Tensor:
+ def sign(self) -> float:
  return 1.0
 
 
@@ -207,6 +208,7 @@ class AffineTransformation(Bijection):
  def __init__(
  self, loc: Optional[Tensor] = None, scale: Optional[Tensor] = None
  ) -> None:
+ super().__init__(self)
  self.loc = loc
  self.scale = scale
 
@@ -233,8 +235,8 @@ def log_abs_det_jac(self, x: Tensor, y: Tensor) -> Tensor:
  return F.zeros_like(x)
 
  @property
- def sign(self):
- return self.scale.sign()
+ def sign(self) -> Union[float, Tensor]:
+ return 1.0 if self.scale is None else self.scale.sign()
 
  @property
  def event_dim(self) -> int: