Python中的 numpy.logaddexp2()

numpy.logaddexp2()函数用于计算以 2 为底的输入的幂和的对数。

当计算的事件概率可能小到超出正常浮点数的范围时，此函数在机器学习中很有用。在这种情况下，可以使用计算概率的以 2 为底的对数。此函数允许添加以这种方式存储的概率。它计算log2(2**x1 + 2**x2) 。

Syntax : numpy.logaddexp2(arr1, arr2, /, out=None, *, where=True, casting=’same_kind’, order=’K’, dtype=None, ufunc ‘logaddexp’)

Parameters :
arr1 : [array_like] Input array.
arr2 : [array_like] Input array.
out : [ndarray, optional] A location into which the result is stored.
  -> If provided, it must have a shape that the inputs broadcast to.
  -> If not provided or None, a freshly-allocated array is returned.
where : [array_like, optional] True value means to calculate the universal functions(ufunc) at that position, False value means to leave the value in the output alone.
**kwargs : allows you to pass keyword variable length of argument to a function. It is used when we want to handle named argument in a function.

Return : [ndarray or scalar] It returns Base-2 logarithm of 2**x1 + 2**x2. This is a scalar if both arr1 and arr2 are scalars.

代码#1：

# Python3 code demonstrate logaddexp2() function
  
# importing numpy
import numpy as geek
  
in_num1 = 2
in_num2 = 3
print ("Input  number1 : ", in_num1)
print ("Input  number2 : ", in_num2)
  
out_num = geek.logaddexp2(in_num1, in_num2)
print ("Output number : ", out_num)

输出 ：

Input  number1 :  2
Input  number2 :  3
Output number :  3.58496250072

代码#2：

# Python3 code demonstrate logaddexp2() function
  
# importing numpy
import numpy as geek
  
in_arr1 = [2, 3, 8] 
in_arr2 = [1, 2, 3]
print ("Input array1 : ", in_arr1) 
print ("Input array2 : ", in_arr2)
    
out_arr = geek.logaddexp2(in_arr1, in_arr2) 
print ("Output array : ", out_arr) 

输出 ：

Input array1 :  [2, 3, 8]
Input array2 :  [1, 2, 3]
Output array :  [ 2.5849625   3.5849625   8.04439412]