Unexpectedly variable result

[IanCarr]

BPO	38869
Nosy	@zware
Files	bug.py: Example

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2019-11-20.21:43:28.804>
created_at = <Date 2019-11-20.21:32:48.824>
labels = ['type-bug']
title = 'Unexpectedly variable result'
updated_at = <Date 2019-11-20.21:43:28.791>
user = 'https://bugs.python.org/IanCarr'

bugs.python.org fields:

activity = <Date 2019-11-20.21:43:28.791>
actor = 'zach.ware'
assignee = 'none'
closed = True
closed_date = <Date 2019-11-20.21:43:28.804>
closer = 'zach.ware'
components = []
creation = <Date 2019-11-20.21:32:48.824>
creator = 'IanCarr'
dependencies = []
files = ['48727']
hgrepos = []
issue_num = 38869
keywords = []
message_count = 2.0
messages = ['357105', '357106']
nosy_count = 2.0
nosy_names = ['zach.ware', 'IanCarr']
pr_nums = []
priority = 'normal'
resolution = 'third party'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue38869'
versions = ['Python 2.7']

[IanCarr]

I can't understand why the result of changes() in the example file changes. I get:
[[6.90642211e-310]
[1.01702662e-316]
[1.58101007e-322]]
[[0.]
[0.]
[0.]]
with an Ubuntu 14 system that has had a lot of changes made. I've checked the same happens on pythonanywhere.com so it does not seem to just be my system is broken. I wondered if there was some strange state in cv2 I don't know about, but as commenting out the tvec=np.zeros(3) line removes the behaviour I think there is something strange here. Now I've got it down to a few lines I can find a work around and obviously numpy and opencv are huge packages and it may be in their court, but I think it is worth someone taking a look who knows more than me.
Yours
Ian

[zware]

I don't see anything here to indicate a bug in CPython or the standard library, so I'm closing the issue. I would recommend asking for help with this on python-list@python.org (comp.lang.python) or StackOverflow. If you can reduce it to a bug in either numpy or cv2, you'll need to report it to the correct issue tracker for the project.