mindspore.nn.probability.distribution.HalfNormal

class mindspore.nn.probability.distribution.HalfNormal(mean=None, sd=None, seed=None, dtype=mstype.float32, name='HalfNormal')

HalfNormal distribution. A HalfNormal distribution is a continuous distribution with the range $[\mu ,inf)$ and the probability density function:

$$f(x,\mu ,\sigma )=1/\sigma \sqrt{2\pi }\exp (-(x-\mu {)}^2/2{\sigma }^2).$$

where $\mu ,\sigma$ are the mean and the standard deviation of the half normal distribution respectively.

Parameters

• mean (Union[int, float, list, numpy.ndarray, Tensor], optional) – The mean of the distribution. $\mu$ in the formula. If this arg is None , then the mean of the distribution will be passed in runtime. Default: None .

• sd (Union[int, float, list, numpy.ndarray, Tensor], optional) – The standard deviation of the distribution. $\sigma$ in the formula. If this arg is None , then the sd of the distribution will be passed in runtime. Default: None .

• seed (int, optional) – The seed used in sampling. The global seed is used if it is None. Default: None .

• dtype (mindspore.dtype, optional) – The type of the event samples. Default: mstype.float32 .

• name (str, optional) – The name of the distribution. Default: 'HalfNormal' .

Note

• sd must be greater than zero.

• dtype must be a float type because HalfNormal distributions are continuous.

• If the arg mean or sd is passed in runtime, then it will be used as the parameter value. Otherwise, the value passed in the constructor will be used.

Raises

• ValueError – When sd <= 0.

• TypeError – When the input dtype is not a float or a subclass of float.

Supported Platforms:

CPU

Examples

>>> import mindspore
>>> import mindspore.nn as nn
>>> from mindspore.nn.probability.distribution import HalfNormal
>>> from mindspore import Tensor
>>> # To initialize a HalfNormal distribution of the mean 3.0 and the standard deviation 4.0.
>>> n1 = HalfNormal(3.0, 4.0, dtype=mindspore.float32)
>>> # A HalfNormal distribution can be initialized without arguments.
>>> # In this case, `mean` and `sd` must be passed in through arguments.
>>> hn = HalfNormal(dtype=mindspore.float32)
>>> # Here are some tensors used below for testing
>>> value = Tensor([1.0, 2.0, 3.0], dtype=mindspore.float32)
>>> mean_a = Tensor([2.0], dtype=mindspore.float32)
>>> sd_a = Tensor([2.0, 2.0, 2.0], dtype=mindspore.float32)
>>> mean_b = Tensor([1.0], dtype=mindspore.float32)
>>> sd_b = Tensor([1.0, 1.5, 2.5], dtype=mindspore.float32)
>>> ans = n1.log_prob(value)
>>> print(ans.shape)
(3,)
>>> # Evaluate with respect to the distribution b.
>>> ans = n1.log_prob(value, mean_b, sd_b)
>>> print(ans.shape)
(3,)
>>> # `mean` and `sd` must be passed in during function calls
>>> ans = hn.log_prob(value, mean_a, sd_a)
>>> print(ans.shape)
(3,)

log_prob(value, mean=None, sd=None)

Evaluate log probability of the value of the HalfNormal distribution.

Parameters

• value (Tensor) - the value to compute.

• mean (Tensor, optional) - the mean of the distribution. Default: None .

• sd (Tensor, optional) - the standard deviation of the distribution. Default: None .

Returns

Tensor, the log value of the probability.