SymPy 根据另一个表达变量 [英] SymPy express variable in terms of another

问题描述

我正在使用 Python 的 SymPy 库.我有两个 sympy 符号和表达式来绑定它们:

I am using SymPy lib for Python. I have two sympy symbols and expression that binds them:

x = Symbol('x')
y = Symbol('y')
expr = 2 * x - 7 * y

我如何用x"来表达y"，即获得相等性:

How can i express 'y' in terms of 'x', i.e get the equality:

y = (2/7) * x

谢谢.

推荐答案

这是你如何用 x 来表达这个方程:

This is how you can express this equation in terms of x:

In [1]: from sympy import *

In [2]: x, y = symbols('x, y')

In [3]: expr = 2*x - 7*y

In [4]: solve(expr, y)
Out[4]: [2*x/7]

这是可行的，因为如果 solve() 函数提供的不是完整方程，它会假定提供的表达式等于 0.换句话说，写

This works because if the solve() function is presented with something that is not a full equation, it assumes that the provided expression is equal to zero. In other words, writing

expr = 2*x - 7*y

上面相当于写

expr = Eq(2*x - 7*y, 0)

这会告诉 SymPy

which would tell SymPy that

2x - 7y = 0.

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