python solve Cubic equation without using sympy-CodePudding

Is it possible to solve Cubic equation without using sympy?

Example:

import sympy as sp
xp = 30
num = xp   4.44
sp.var('x, a, b, c, d')
Sol3 = sp.solve(0.0509 * x ** 3   0.0192 * x ** 2   3.68 * x - num, x)

The result is:

[6.07118098358257, -3.2241955998463 - 10.0524891203436*I, -3.2241955998463   10.0524891203436*I]

But I want to find a way to do it with numpy or without 3 part lib at all

I tried with numpy:

import numpy as np
coeff = [0.0509, 0.0192, 3.68, --4.44]
print(np.roots(coeff))

But the result is :

[ 0.40668245 8.54994773j  0.40668245-8.54994773j -1.19057511 0.j]

CodePudding user response：

In your numpy method you are making two slight mistakes with the final coefficient.

In the SymPy example your last coefficient is - num, this is, according to your code: -num = - (xp 4.44) = -(30 4.44) = -34.44

In your NumPy example yout last coefficient is --4.44, which is 4.44 and does not equal -34.33.

If you edit the NumPy code you will get:

import numpy as np
coeff = [0.0509, 0.0192, 3.68, -34.44]
print(np.roots(coeff))
[-3.2241956  10.05248912j -3.2241956 -10.05248912j
  6.07118098  0.j        ]

The answer are thus the same (note that NumPy uses j to indicate a complex number. SymPy used I)

CodePudding user response：

You could implement the

this Youtube video from mathologer could help understand it.