Python中的 numpy.log2()

numpy.log2(arr, out = None, *, where = True, cast = 'same_kind', order = 'K', dtype = None, ufunc 'log1p') ：
这个数学函数帮助用户计算x 的 Base-2 对数，其中 x 属于所有输入数组元素。

参数 ：

array    : [array_like]Input array or object.
out      : [ndarray, optional]Output array with same dimensions as Input array, 
           placed with result.
**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.
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.

返回 ：

An array with Base-2 logarithmic value of x; 
where x belongs to all elements of input array. 

代码 1：工作

# Python program explaining
# log2() function
import numpy as np
  
in_array = [1, 3, 5, 2**8]
print ("Input array : ", in_array)
  
out_array = np.log2(in_array)
print ("Output array : ", out_array)
  
  
print("\nnp.log2(4**4) : ", np.log2(4**4))
print("np.log2(2**8) : ", np.log2(2**8))

输出 ：

Input array :  [1, 3, 5, 256]
Output array :  [ 0.          1.5849625   2.32192809  8.        ]

np.log2(4**4) :  8.0
np.log2(2**8) :  8.0

代码 2：图形表示

# Python program showing
# Graphical representation of 
# log2() function
import numpy as np
import matplotlib.pyplot as plt
  
in_array = [1, 1.2, 1.4, 1.6, 1.8, 2]
out_array = np.log2(in_array)
  
print ("out_array : ", out_array)
  
plt.plot(in_array, in_array, color = 'blue', marker = "*")
  
# red for numpy.log2()
plt.plot(out_array, in_array, color = 'red', marker = "o")
plt.title("numpy.log2()")
plt.xlabel("out_array")
plt.ylabel("in_array")
plt.show()  

输出 ：

out_array :  [ 0.          0.26303441  0.48542683  0.67807191  0.84799691  1.        ]

参考 ：
https://docs.scipy.org/doc/numpy-1.13.0/reference/generated/numpy.exp.html
.