Python numpy.log2()用法及代码示例

numpy.log2(arr，out =无，*，其中= True，强制转换='same_kind'，order ='K'，dtype = None，ufunc'log1p')：
此数学函数可帮助用户计算x的以2为底的对数，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.        ]

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