尝试求解简单的代数方程时，sympy挂起 [英] sympy hangs when trying to solve a simple algebraic equation

问题描述

我最近重新安装了我的python环境，现在可以很好地运行的代码现在可以正常运行了(通常只是挂起，占用了越来越多的内存).

I recently reinstalled my python environment and a code that used to work very quickly now creeps at best (usually just hangs taking up more and more memory).

代码的挂起点是:

solve(exp(-alpha * x**2) - 0.01, alpha)

我已经能够通过全新的IPython 0.13.1会话重现此问题:

I've been able to reproduce this problem with a fresh IPython 0.13.1 session:

In [1]: from sympy import solve, Symbol, exp
In [2]: x = 14.7296138519
In [3]: alpha = Symbol('alpha', real=True)
In [4]: solve(exp(-alpha * x**2) - 0.01, alpha)

这适用于整数，但也很慢.在原始代码中，我遍历了这个过程，以查找数百个不同的x值(除了14.7296138519之外)的alpha，并且花费的时间不超过一秒钟.

this works for integers but also quite slow. In the original code I looped over this looking for hundreds of different alpha's for different values of x (other than 14.7296138519) and it didn't take more than a second.

有什么想法吗?

推荐答案

在这种情况下，引入了Rational = False标志.

The rational=False flag was introduced for such cases as this.

>>> q=14.7296138519
>>> solve(exp(-alpha * q**2) - 0.01, alpha, rational=False)
[0.0212257459123917]

(上面提到的问题中给出了解释.)

(The explanation is given in the issue cited above.)

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