地址：https://github.com/ototsuyume/function-s-root
先把输入的方程解析成语法树，然后求导数，再用牛顿迭代法循环求解，例如：
./parse.py "x^2-20000"
['x', '^', '2', '-', '20000']
<expr.sub_expr object at 0x108301510>
('before differention:', '(x^(2))-20000')
('Differention:', '1*2*(x^(1))-0')
('Simplify:', '2*x')
Iterating times:1 value:10000.500000
Iterating times:2 value:5001.249950
Iterating times:3 value:2502.624475
Iterating times:4 value:1255.308043
Iterating times:5 value:635.620194
Iterating times:6 value:333.542762
Iterating times:7 value:196.752544
Iterating times:8 value:149.201536
Iterating times:9 value:141.624207
Iterating times:10 value:141.421502
Iterating times:11 value:141.421356
The root of the function is:141.421356
存在一个问题是不知道怎么找出第一次迭代时比较好的x值，用随机数发现很容易超出python的整数范围，于是设了初始值为1,看来对大部分的方程都有效，hmmmmmm
比较少用python，代码风格或许不好，望轻喷
先把输入的方程解析成语法树，然后求导数，再用牛顿迭代法循环求解，例如：
./parse.py "x^2-20000"
['x', '^', '2', '-', '20000']
<expr.sub_expr object at 0x108301510>
('before differention:', '(x^(2))-20000')
('Differention:', '1*2*(x^(1))-0')
('Simplify:', '2*x')
Iterating times:1 value:10000.500000
Iterating times:2 value:5001.249950
Iterating times:3 value:2502.624475
Iterating times:4 value:1255.308043
Iterating times:5 value:635.620194
Iterating times:6 value:333.542762
Iterating times:7 value:196.752544
Iterating times:8 value:149.201536
Iterating times:9 value:141.624207
Iterating times:10 value:141.421502
Iterating times:11 value:141.421356
The root of the function is:141.421356
存在一个问题是不知道怎么找出第一次迭代时比较好的x值，用随机数发现很容易超出python的整数范围，于是设了初始值为1,看来对大部分的方程都有效，hmmmmmm
比较少用python，代码风格或许不好，望轻喷
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