python - PyTorch 阶乘函数

Question

似乎没有用于计算阶乘的 PyTorch 函数。在 PyTorch 中有没有办法做到这一点？我希望在 Torch 中手动计算泊松分布(我知道这存在:https://pytorch.org/docs/stable/generated/torch.poisson.html)，并且该公式需要分母中的阶乘。
泊松分布:https://en.wikipedia.org/wiki/Poisson_distribution

Answer 1

我想你可以找到它作为torch.jit._builtins.math.factorial 但是 pytorch以及 numpy和 scipy ( Factorial in numpy and scipy ) 使用 python的内置 math.factorial :

import math

import numpy as np
import scipy as sp
import torch


print(torch.jit._builtins.math.factorial is math.factorial)
print(np.math.factorial is math.factorial)
print(sp.math.factorial is math.factorial)

True
True
True

但是，相比之下， scipy除了“主流” math.factorial包含非常“特殊”的阶乘函数 scipy.special.factorial .与 math 中的函数不同它在数组上运行的模块:

from scipy import special

print(special.factorial is math.factorial)

False

# the all known factorial functions
factorials = (
    math.factorial,
    torch.jit._builtins.math.factorial,
    np.math.factorial,
    sp.math.factorial,
    special.factorial,
)

# Let's run some tests
tnsr = torch.tensor(3)

for fn in factorials:
    try:
        out = fn(tnsr)
    except Exception as err:
        print(fn.__name__, fn.__module__, ':', err)
    else:
        print(fn.__name__, fn.__module__, ':', out)

factorial math : 6
factorial math : 6
factorial math : 6
factorial math : 6
factorial scipy.special._basic : tensor(6., dtype=torch.float64)

tnsr = torch.tensor([1, 2, 3])

for fn in factorials:
    try:
        out = fn(tnsr)
    except Exception as err:
        print(fn.__name__, fn.__module__, ':', err)
    else:
        print(fn.__name__, fn.__module__, ':', out)

factorial math : only integer tensors of a single element can be converted to an index
factorial math : only integer tensors of a single element can be converted to an index
factorial math : only integer tensors of a single element can be converted to an index
factorial math : only integer tensors of a single element can be converted to an index
factorial scipy.special._basic : tensor([1., 2., 6.], dtype=torch.float64)