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- """
- Ross Wightman
- https://github.com/rwightman/pytorch-image-models
- """
- import torch
- import math
- import warnings
- import collections
- from itertools import repeat
-
- def _no_grad_trunc_normal_(tensor, mean, std, a, b):
- # Cut & paste from PyTorch official master until it's in a few official releases - RW
- # Method based on https://people.sc.fsu.edu/~jburkardt/presentations/truncated_normal.pdf
- def norm_cdf(x):
- # Computes standard normal cumulative distribution function
- return (1. + math.erf(x / math.sqrt(2.))) / 2.
-
- if (mean < a - 2 * std) or (mean > b + 2 * std):
- warnings.warn("mean is more than 2 std from [a, b] in nn.init.trunc_normal_. "
- "The distribution of values may be incorrect.",
- stacklevel=2)
-
- with torch.no_grad():
- # Values are generated by using a truncated uniform distribution and
- # then using the inverse CDF for the normal distribution.
- # Get upper and lower cdf values
- l = norm_cdf((a - mean) / std)
- u = norm_cdf((b - mean) / std)
-
- # Uniformly fill tensor with values from [l, u], then translate to
- # [2l-1, 2u-1].
- tensor.uniform_(2 * l - 1, 2 * u - 1)
-
- # Use inverse cdf transform for normal distribution to get truncated
- # standard normal
- tensor.erfinv_()
-
- # Transform to proper mean, std
- tensor.mul_(std * math.sqrt(2.))
- tensor.add_(mean)
-
- # Clamp to ensure it's in the proper range
- tensor.clamp_(min=a, max=b)
- return tensor
-
-
- def trunc_normal_(tensor, mean=0., std=1., a=-2., b=2.):
- # type: (Tensor, float, float, float, float) -> Tensor
- r"""Fills the input Tensor with values drawn from a truncated
- normal distribution. The values are effectively drawn from the
- normal distribution :math:`\mathcal{N}(\text{mean}, \text{std}^2)`
- with values outside :math:`[a, b]` redrawn until they are within
- the bounds. The method used for generating the random values works
- best when :math:`a \leq \text{mean} \leq b`.
- Args:
- tensor: an n-dimensional `torch.Tensor`
- mean: the mean of the normal distribution
- std: the standard deviation of the normal distribution
- a: the minimum cutoff value
- b: the maximum cutoff value
- Examples:
- >>> w = torch.empty(3, 5)
- >>> nn.init.trunc_normal_(w)
- """
- return _no_grad_trunc_normal_(tensor, mean, std, a, b)
-
-
- # From PyTorch internals
- def _ntuple(n):
- def parse(x):
- if isinstance(x, collections.abc.Iterable):
- return x
- return tuple(repeat(x, n))
- return parse
-
-
- to_1tuple = _ntuple(1)
- to_2tuple = _ntuple(2)
- to_3tuple = _ntuple(3)
- to_4tuple = _ntuple(4)
- to_ntuple = _ntuple
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