class_docstr: The Half Normal distribution with scale `scale`.
  
  #### Mathematical details
  
  The half normal is a transformation of a centered normal distribution.
  If some random variable `X` has normal distribution,
  ```none
  X ~ Normal(0.0, scale)
  Y = |X|
  ```
  Then `Y` will have half normal distribution. The probability density
  function (pdf) is:
  
  ```none
  pdf(x; scale, x > 0) = sqrt(2) / (scale * sqrt(pi)) *
    exp(- 1/2 * (x / scale) ** 2)
  )
  ```
  Where `scale = sigma` is the standard deviation of the underlying normal
  distribution.
  
  #### Examples
  
  Examples of initialization of one or a batch of distributions.
  
  ```python
  # Define a single scalar HalfNormal distribution.
  dist = tfp.distributions.HalfNormal(scale=3.0)
  
  # Evaluate the cdf at 1, returning a scalar.
  dist.cdf(1.)
  
  # Define a batch of two scalar valued HalfNormals.
  # The first has scale 11.0, the second 22.0
  dist = tfp.distributions.HalfNormal(scale=[11.0, 22.0])
  
  # Evaluate the pdf of the first distribution on 1.0, and the second on 1.5,
  # returning a length two tensor.
  dist.prob([1.0, 1.5])
  
  # Get 3 samples, returning a 3 x 2 tensor.
  dist.sample([3])
  ```
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docstr: Distribution parameter for the scale.
docstr_tok: ["Distribution","parameter","for","the","scale","."]
code: def scale(self):
      """Distribution parameter for the scale."""
      return self._scale
  
imports: import math
  import numpy
  import tensorflow.compat.v2
  from tensorflow_probability.python.bijectors import softplus
  from tensorflow_probability.python.distributions import distribution
  from tensorflow_probability.python.distributions import kullback_leibler
  from tensorflow_probability.python.internal import assert_util
  from tensorflow_probability.python.internal import dtype_util
  from tensorflow_probability.python.internal import parameter_properties
  from tensorflow_probability.python.internal import prefer_static
  from tensorflow_probability.python.internal import reparameterization
  from tensorflow_probability.python.internal import samplers
  from tensorflow_probability.python.internal import tensor_util
label_desc: Use image node_id 3 for calling the HalfNormal obj's underlying member method code with example usage: obj.scale() and returns: self