numpy.arccos() in Python

Last Updated : 29 Nov, 2018

numpy.arccos(x[, out]) = ufunc ‘arccos’) : This mathematical function helps user to calculate inverse cos for all x(being the array elements).

Parameters :

array    : [array_like]elements are in radians.
out      : [array_like]array of same shape as x.

Note :

2pi Radians = 360 degrees
The convention is to return the angle z whose real part lies in [0, pi].

Return :

An array with inverse cosine of x 
for all x i.e. array elements. 

The values are in the closed interval [-pi/2, pi/2].

Code #1 : Working

# Python program explaining 
# arccos() function 
  
import numpy as np 
  
in_array = [0, 1, 0.3, -1] 
print ("Input array : \n", in_array) 
  
arccos_Values = np.arccos(in_array) 
print ("\nInverse Cosine values : \n", arccos_Values) 

Output :

Input array : 
 [0, 1, 0.3, -1]

Inverse Cosine values : 
 [ 1.57079633  0.          1.26610367  3.14159265]

Code #2 : Graphical representation

# Python program showing 
# Graphical representation   
# of arccos() function 
  
import numpy as np 
import matplotlib.pyplot as plt 
  
in_array = np.linspace(-np.pi, np.pi, 12) 
out_array1 = np.cos(in_array) 
out_array2 = np.arccos(in_array) 
  
print("in_array : ", in_array) 
print("\nout_array with cos : ", out_array1) 
print("\nout_arraywith arccos : ", out_array1) 
  
# red for numpy.arccos() 
plt.plot(in_array, out_array1, 
            color = 'blue', marker = "*") 
              
plt.plot(in_array, out_array2, 
            color = 'red', marker = "o") 
              
plt.title("blue : numpy.cos() \nred : numpy.arccos()") 
plt.xlabel("X") 
plt.ylabel("Y") 
plt.show() 

Output :


in_array :  [-3.14159265 -2.57039399 -1.99919533 -1.42799666 -0.856798   -0.28559933
  0.28559933  0.856798    1.42799666  1.99919533  2.57039399  3.14159265]

out_array with cos :  [-1.         -0.84125353 -0.41541501  0.14231484  0.65486073  0.95949297
  0.95949297  0.65486073  0.14231484 -0.41541501 -0.84125353 -1.        ]

out_arraywith arccos :  [-1.         -0.84125353 -0.41541501  0.14231484  0.65486073  0.95949297
  0.95949297  0.65486073  0.14231484 -0.41541501 -0.84125353 -1.        ]
RuntimeWarning: invalid value encountered in arccos
  out_array1 = np.sin(in_array)

References :
https://docs.scipy.org/doc/numpy-dev/reference/generated/numpy.arcsin.html#numpy.arccos
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