Python中的 sympy.stats.MultivariateEwens()函数

借助sympy.stats.MultivariateEwens()方法，我们可以创建具有多元 Ewens 分布的离散随机变量。

Syntax: sympy.stats.MultivariateEwens(syms, n, theta)

Parameters:
 syms: the symbol
 n: size of the sample or the integer whose partitions are considered, a positive integer
 theta: mutation rate, must be positive real number

Returns: a discrete random variable with Multivariate Ewens Distribution.

示例 #1：

Python3

# import sympy, MultivariateEwens, density, Symbol
from sympy.stats.joint_rv_types import MultivariateEwens
from sympy.stats import density
from sympy import Symbol, pprint
  
a = Symbol('a', positive = True)
b = Symbol('b', positive = True)
  
# using sympy.stats.MultivariateEwens() method
E = MultivariateEwens('E', 2, 1)
mveDist = density(E)(a, b)
  
pprint(mveDist)

输出 ：

/   -a2                    
|  2                       
|-------  for a1 + 2*a2 = 2

示例 #2：

Python3

# import sympy, MultivariateEwens, density, Symbol
from sympy.stats.joint_rv_types import MultivariateEwens
from sympy.stats import density
from sympy import Symbol, pprint
  
a = Symbol('a', positive = True)
b = Symbol('b', positive = True)
  
# using sympy.stats.MultivariateEwens() method
E = MultivariateEwens('E', 2, 1 / 2)
mveDist = density(E)(a, b)
  
pprint(mveDist)

输出 ：

/   -a1  -2*a2                   
|8*2   *2                        
|-------------  for a1 + 2*a2 = 2
<  3*a1!*a2!                     
|                                
|      0            otherwise    
\