RankWarning: Polyfit may be poorly conditioned问题的解决

本人系统为MacOS catalina 10.15.7

新的MacBook pro 用brew install python 安装了python，自动为3.9.0版本。然后pip3 install notebook，安装了jupyter noteboook。随后pip3 install numpy，打开notebook，出现“RankWarning: Polyfit may be poorly conditioned“ 错误。

import numpy as np
---------------------------------------------------------------------------
RuntimeError                              Traceback (most recent call last)
<ipython-input-5-0aa0b027fcb6> in <module>
----> 1 import numpy as np

/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/site-packages/numpy/__init__.py in <module>
    284                     "that provided NumPy.\n{}\n".format(
    285                         error_message))
--> 286                 raise RuntimeError(msg)
    287     del _mac_os_check
    288 

RuntimeError: Polyfit sanity test emitted a warning, most likely due to using a buggy Accelerate backend. If you compiled yourself, see site.cfg.example for information. Otherwise report this to the vendor that provided NumPy.
RankWarning: Polyfit may be poorly conditioned

查了一圈儿，发现是因为我的python 版本太高3.9的问题，回滚到3.8就没问题了。因此卸载了python 3.9 ，使用mac自带的python 3.8 重新安装即可。

注意，python3.9的卸载需要卸载完全，包括依赖包和软链接接，都要卸载干净。具体过程见本人文章 如何彻底卸载mac上的python 3.9

安装numpy

在mac默认的（或者自己重新装的）python 3.8的环境下安装numpy：

$ pip3 install numpy
Collecting numpy
  Downloading https://files.pythonhosted.org/packages/33/1a/d10d1c23d21c289a3e87e751a9daf0907e91665cab08d0c35033fd4f5b55/numpy-1.19.2-cp38-cp38-macosx_10_9_x86_64.whl (15.3MB)
     |████████████████████████████████| 15.3MB 12.1MB/s 
Installing collected packages: numpy
ERROR: Could not install packages due to an EnvironmentError: [Errno 13] Permission denied: '/Library/Python/3.8'
Consider using the `--user` option or check the permissions.

出现权限问题

改用root权限安装

$sudo pip3 install numpy
Password:
.......
https://files.pythonhosted.org/packages/33/1a/d10d1c23d21c289a3e87e751a9daf0907e91665cab08d0c35033fd4f5b55/numpy-1.19.2-cp38-cp38-macosx_10_9_x86_64.whl (15.3MB)
     |████████████████████████████████| 15.3MB 414kB/s 
Installing collected packages: numpy
Successfully installed numpy-1.19.2

安装成功
还可以使用pip3 install numpy --user 也可。这种安装只能登陆的账户使用。