用 SymPy 求解方程组 [英] Solving Systems of Equations with SymPy

问题描述

我正在尝试使用 SymPy 0.7.1 求解一组方程:

from sympy import *方程 = [Eq(S('vf'), S('vi + a*t')),Eq(S('d'), S('vi*t + 1/2*a*t**2')),等式(S('a'), S('10')),等式(S('d'), S('60')),等式(S('vi'), S('5'))]打印解决(方程)

产生正确的结果，但顺序奇怪:

[(-4, 10, 60, -35, 5), (3, 10, 60, 35, 5)]

如何确定哪个值适合哪个变量?变量顺序似乎是任意的.文档建议提供额外的参数:

print solve(equations, var('a'), var('d'), var('t'), var('vi'), var('vf'))

但这似乎没有效果.

在此先感谢您的帮助！

解决方案

我也无法弄清楚输出.最初我认为问题是因为您正在创建新的 var 对象而不是重用原始对象，但事实证明并非如此.如果可能的话，我会简单地升级到 0.7.1-git，那里的表现要好得多:

<预><代码>>>>进口同情>>>同情.__版本__'0.7.1-git'>>>from sympy import S, Eq, solve>>>>>>vf, d, a, vi, t = S('vf d a vi t'.split())>>>方程 = [... Eq(vf, vi+a*t),... Eq(d, vi*t + a*t**2/2),... 等式(a, 10),... 等式(d，60)，... 等式(vi, 5)]>>>>>>解决(方程)[{vf:-35，t:-4，a:10，vi:5，d:60}，{vf:35，t:3，a:10，vi:5，d:60}]>>>解决(方程，[a，t，vi，vf，d])[(10, -4, 5, -35, 60), (10, 3, 5, 35, 60)]

默认情况下不错的词典，并指定顺序有效.

I'm trying to solve a set of equations with SymPy 0.7.1:

from sympy import *
equations = [
    Eq(S('vf'), S('vi + a*t')),
    Eq(S('d'), S('vi*t + 1/2*a*t**2')),
    Eq(S('a'), S('10')),
    Eq(S('d'), S('60')),
    Eq(S('vi'), S('5'))
]
print solve(equations)

produces the correct result, but in a strange order:

[(-4, 10, 60, -35, 5), (3, 10, 60, 35, 5)]

How can I identify which value fits which variable? The variable order seems arbitrary. The documentation suggests providing additional arguments:

print solve(equations, var('a'), var('d'), var('t'), var('vi'), var('vf'))

But this seems to have no effect.

Thanks in advance for any help!

解决方案

I can't figure out the outputs either. Originally I thought the problem was because you were creating new var objects rather than reusing the original ones, but that turned out not to be it. If possible, I'd simply upgrade to 0.7.1-git, where things are much better behaved:

>>> import sympy
>>> sympy.__version__
'0.7.1-git'
>>> from sympy import S, Eq, solve
>>> 
>>> vf, d, a, vi, t = S('vf d a vi t'.split())
>>> equations = [
...     Eq(vf, vi+a*t),
...     Eq(d, vi*t + a*t**2/2),
...     Eq(a, 10),
...     Eq(d, 60),
...     Eq(vi, 5)]
>>> 
>>> solve(equations)
[{vf: -35, t: -4, a: 10, vi: 5, d: 60}, {vf: 35, t: 3, a: 10, vi: 5, d: 60}]
>>> solve(equations, [a, t, vi, vf, d])
[(10, -4, 5, -35, 60), (10, 3, 5, 35, 60)]

Nice dictionaries by default, and specifying the order works.

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