Python| sympy.ff() 方法

在sympy.ff()方法的帮助下，我们可以找到下降阶乘。下降阶乘定义为 –

$ff(x, k) = x \cdot (x-1) \cdots (x-k+1)$

其中x可以是任意表达式， k是整数。

Syntax: ff(x, k)

Parameter:
x – It denotes any arbitrary expression.
k – It denotes an integer.

Returns: Returns falling factorial corresponding to the given inputs.

示例 #1：

# import sympy 
from sympy import * 
  
x = symbols('x')
k = 5
print("Value of x = {} and k = {}".format(x, k))
   
# Use sympy.ff() method 
ff_x_k = ff(x, k)  
      
print("Falling factorial ff(x, k) : {}".format(ff_x_k))  

输出：

Value of x = x and k = 5
Falling factorial ff(x, k) : x*(x - 4)*(x - 3)*(x - 2)*(x - 1)

示例 #2：

# import sympy 
from sympy import * x = 7
k = 5
print("Value of x = {} and k = {}".format(x, k))
   
# Use sympy.ff() method 
ff_x_k = ff(x, k)  
      
print("Falling factorial ff(x, k) : {}".format(ff_x_k))  

输出：

Value of x = 7 and k = 5
Falling factorial ff(x, k) : 2520