问题描述
当我运行这个程序时，我最终没有得到解决方案，但应该有一个解决方案(我相信).知道我做错了什么吗?如果你从 e2 方程中去掉 Q，它似乎可以正常工作.
When I run this program, I get no solution at the end, but there should be a solution ( I believe). Any idea what I am doing wrong? If you take away the Q from e2 equation it seems to work correctly.
#!/usr/bin/python
from sympy import *
a,b,w,r = symbols('a b w r',real=True,positive=True)
L,K,Q = symbols('L K Q',real=True,positive=True)
e1=K
e2=(K*Q/2)**(a)
print solve(e1-e2,K)
如果我们执行以下操作，它会起作用:
It works if we do the following:
- 设置 Q=1 或，
- 将 e2 改为 e2=(K*a)(Q/2)**(a)
- Set Q=1 or,
- Change e2 to e2=(K*a)(Q/2)**(a)
不过，我仍然希望它以原始方式工作，因为我的方程比这更复杂.
I would still like it to work in the original way though, as my equations are more complicated than this.
推荐答案
这只是solve的一个不足.solve 主要基于启发式算法，因此有时当方程以特定形式给出时，它无法弄清楚如何求解.这里的解决方法是在表达式上调用 expand_power_base，因为 SymPy 能够解决 K - K**a*(Q/2)**a:>
This is just a deficiency of solve. solve is based mostly on heuristics, so sometimes it isn't able to figure out how to solve an equation when it's given in a particular form. The workaround here is to just call expand_power_base on the expression, since SymPy is able to solve K - K**a*(Q/2)**a:
In [8]: print(solve(expand_power_base(e1-e2),K))
[(2/Q)**(a/(a - 1))]
还值得指出的是，solve 的 [] 的结果 并不 以任何方式意味着没有解决方案，只有solve 无法找到任何.请参阅 http://docs.sympy.org/latest/tutorial/solvers 上的第一条注释.html.
It's also worth pointing out that the result of [] from solve does not in any way mean that there are no solutions, only that solve was unable to find any. See the first note at http://docs.sympy.org/latest/tutorial/solvers.html.
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