问在Sympy上增加两个泊松的计算是非常缓慢的。

EN

import sympy as sp
import sympy.stats as ss
x= ss.Poisson("x", 3)
y = ss.Poisson("y", 6)
mixed = x+y
d = ss.density(mixed)

# substitute infinity with a symbol
n = sp.symbols("n")
expr = d(0).subs(sp.oo, n)

# generate a function to be evaluate with Numpy/Scipy
f = sp.lambdify([n], expr)

# evaluate the function: provide a relatively high value of `n`
print(f(100))
# out: 0.00012340980408667956

print(f(400))
# OverflowError: int too large to convert to float

In [25]: d(0)
Out[25]: 
  ∞                          
______                       
╲                            
 ╲                           
  ╲    ⎧ -y  y  -9           
   ╲   ⎪3  ⋅6 ⋅ℯ             
    ╲  ⎪──────────  for y ≤ 0
    ╱  ⎨ (-y)!⋅y!            
   ╱   ⎪                     
  ╱    ⎪    0       otherwise
 ╱     ⎩                     
╱                            
‾‾‾‾‾‾                       
y = 0 

In [29]: d(0).args[0].subs(y.symbol, 0)
Out[29]: 
 -9
ℯ  

In [30]: ss.density(x)(0) * ss.density(y)(0)
Out[30]: 
 -9
ℯ  

In [31]: ss.P(Eq(x, 0) & Eq(y, 0))
Out[31]: 
 -9
ℯ 

In [32]: N(_)
Out[32]: 0.000123409804086680