Orbit propagate get wrong answer

[Rundao]

🐞 Orbit propagate get wrong answer in 3 cases

from poliastro.twobody.propagation.farnocchia import farnocchia_rv_fast as propagate

Case1

propagate(1., np.array([1., -1., 0.]), np.array([-1., -1., 0.]), 0.)
array([[ 1.41421356e+00,  0.00000000e+00,  0.00000000e+00],
       [ 0.00000000e+00, -1.41421356e+00,  1.73191211e-16]])

It should be r = [1., -1., 0.] and v = [-1., -1., 0.]

Case2

propagate(1., np.array([1., 0., 0.]), np.array([-1., -1., 0.]), 0.)

It raises ZeroDivisionError: division by zero.

Case3

propagate(1., np.array([1., 0., 0.]), np.array([-1.1, -1., 0.]), 0.)
array([[ 1.00000000e+00,  8.88178420e-16, -1.08770486e-31],
       [-1.10000000e+00, -1.00000000e+00,  1.22464680e-16]])

is correct, but change vz0=0. to vz0=-0.

propagate(1., np.array([1., 0., 0.]), np.array([-1.1, -1., -0.]), 0.)
array([[-1.00000000e+00, -7.65713740e-16, -1.08770486e-31],
       [ 1.10000000e+00,  1.00000000e+00,  1.22464680e-16]])

it returns -r_correct.

🖥 Please paste the output of following commands

• conda list
  Name Version Build Channel
  poliastro 0.17.0 pyhd8ed1ab_1 conda-forge

# Paste your output here:

# Paste your output here:

💡 Possible solutions

📋 Steps to solve the problem

• Comment below about what you've started working on.
• Add, commit, push your changes
• Submit a pull request and add this in comments - Addresses #<put issue number here>
• Ask for a review in comments section of pull request
• Celebrate your contribution to this project 🎉