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Python | sympy.bell() method

  • Last Updated : 14 Jul, 2019

With the help of sympy.bell() method, we can find Bell number and Bell polynomials in SymPy.

bell(n) -

Syntax: bell(n)

Parameter:
n – It denotes the order of the bell number.

Returns: Returns the nth bell number.

Example #1:




# import sympy 
from sympy import * n = 5
print("Value of n = {}".format(n))
   
# Use sympy.bell() method 
nth_bell = bell(n)  
      
print("Value of nth bell number : {}".format(nth_bell))  

Output:

Value of n = 5
Value of nth bell number : 52

bell(n, k) –

Syntax: bell(n, k)

Parameter:
n – It denotes the order of the bell polynomial.
k – It denotes the variable in the bell polynomial.

Returns: Returns the expression of the bell polynomial or its value.

Example #2:




# import sympy 
from sympy import * n = 5
k = symbols('x')
print("Value of n = {} and k = {}".format(n, k))
   
# Use sympy.bell() method 
nth_bell_poly = bell(n, k)  
      
print("The nth bell polynomial : {}".format(nth_bell_poly))  

Output:

Value of n = 5 and k = x
The nth bell polynomial : x**5 + 10*x**4 + 25*x**3 + 15*x**2 + x

Example #3:




# import sympy 
from sympy import * n = 5
k = 3
print("Value of n = {} and k = {}".format(n, k))
   
# Use sympy.bell() method 
nth_bell_poly = bell(n, k)  
      
print("The nth bell polynomial value : {}".format(nth_bell_poly))  

Output:

Value of n = 5 and k = 3
The nth bell polynomial value : 1866

bell(n, k, (x1, x2, x3, …)) –

Syntax: bell(n, k, (x1, x2, x3, …))

Parameter:
n – It denotes the order of the bell polynomial of second kind.
k – It is a parameter in the bell polynomial of second kind.
(x1, x2, x3, …) – It denotes the tuple of variable symbols.

Returns: Returns the Bell polynomials of the second kind.

Example #4:




# import sympy 
from sympy import * n = 5
k = 3
variables = symbols('x:6')[1:]
print("Value of n = {}, k = {} and variables = {}".format(n, k, variables))
   
# Use sympy.bell() method 
nth_bell_poly = bell(n, k, variables)  
      
print("The nth bell polynomial of second kind : {}".format(nth_bell_poly))  

Output:

Value of n = 5, k = 3 and variables = (x1, x2, x3, x4, x5)
The nth bell polynomial of second kind : 10*x1**2*x3 + 15*x1*x2**2

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