Solving system of equations in python

Question

How do I solve simple system of equation like the following in python?

x = (2/3)*y + (1/3)*0

y = (2/3)*1 + (1/3)*x

I tried SymPy but couldn't figure it out.

solved the equation part

from sympy import *
from sympy.solvers.solveset import linsolve
x, y = symbols('x, y')
linsolve([x - 2/3*y, y - 2/3 - 1/3*x ], (x, y))

Output: {(0.571428571428571, 0.857142857142857)}

Type is 'sympy.sets.sets.FiniteSet'

How do I extract just the x value to set as a variable?

Got it.

z = linsolve([x - 2/3*y, y - 2/3 - 1/3*x ], (x, y))

print(z.args[0][0])

Answer 1

Using numpy python module

Example solving following system of linear equation

Case 1:

24a + 4b = 35

8a + 4b = 94

Case 2:

a + b = 4

2a + b = 8

>>> import numpy as np
>>> a = np.array([[24, 4],[8,4]])
>>> b = np.array([35, 94])
>>> print(np.linalg.solve(a,b))
[-3.6875 30.875 ]
>>> a = np.array([[1, 1],[2,1]])
>>> b = np.array([4, 8])
>>> print(np.linalg.solve(a,b))
[4. 0.]

Answer 2

sympy has updated to solve() for solving the System of linear Equations. first create equations with Eq() method. and then solve those equations with solve(). linsolve() also still works.

import sympy as sp
from sympy.solvers import solve
eq1= sp.Eq(x-2/3*y-1/3*0) 
eq2 = sp.Eq(1/3*x-y+2/3)
output = solve([eq1,eq2],dict=True)

your equations are like this

x?0.666666666666667y=0
0.333333333333333x?y+0.666666666666667=0

output:

[{x:0.571428571428571, y:0.857142857142857}]

once you get the output. output variable type is list. then take the first index 0which is dictionary. then convert it into list type.

values = list(output[0].values())

will give your output like this.

[0.571428571428571, 0.857142857142857]

then

x = values[0] #0.571428571428571
y = values[1] # 0.857142857142857