Raspberry pi 3 type Bにtensorflowをインストールする

raspberry piにtensorflowを入れたので備忘録です。
(間違っているところがありましたら、コメントお願いいたします。)

###ハードウェア
- Raspberry Pi 3 type B

###ソフトウェア
- OS：Ubuntu MATE 16.04.3 LTS
- Tensorflow：1.4.1


###やったこと
このページにあるwhlファイルをダウンロード
https://github.com/lhelontra/tensorflow-on-arm/releases

python 3.5で行った場合、下記の通りインストールします。

```
sudo pip3 install tensorflow-1.4.1-cp35-none-linux_armv7l.whl
```

これでインストールできるが、importをすると、

```
raspi@raspi-desktop:~$ python3
Python 3.5.2 (default, Nov 23 2017, 16:37:01)
[GCC 5.4.0 20160609] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import tensorflow as tf
Traceback (most recent call last):
  File "/usr/local/lib/python3.5/dist-packages/tensorflow/python/pywrap_tensorflow.py", line 58, in <module>
    from tensorflow.python.pywrap_tensorflow_internal import *
  File "/usr/local/lib/python3.5/dist-packages/tensorflow/python/pywrap_tensorflow_internal.py", line 28, in <module>
    _pywrap_tensorflow_internal = swig_import_helper()
  File "/usr/local/lib/python3.5/dist-packages/tensorflow/python/pywrap_tensorflow_internal.py", line 24, in swig_import_helper
    _mod = imp.load_module('_pywrap_tensorflow_internal', fp, pathname, description)
  File "/usr/lib/python3.5/imp.py", line 242, in load_module
    return load_dynamic(name, filename, file)
  File "/usr/lib/python3.5/imp.py", line 342, in load_dynamic
    return _load(spec)
ImportError: /usr/lib/arm-linux-gnueabihf/libstdc++.so.6: version `GLIBCXX_3.4.22' not found (required by /usr/local/lib/python3.5/dist-packages/tensorflow/python/_pywrap_tensorflow_internal.so)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python3.5/dist-packages/tensorflow/__init__.py", line 24, in <module>
    from tensorflow.python import *
  File "/usr/local/lib/python3.5/dist-packages/tensorflow/python/__init__.py", line 49, in <module>
    from tensorflow.python import pywrap_tensorflow
  File "/usr/local/lib/python3.5/dist-packages/tensorflow/python/pywrap_tensorflow.py", line 72, in <module>
    raise ImportError(msg)
ImportError: Traceback (most recent call last):
  File "/usr/local/lib/python3.5/dist-packages/tensorflow/python/pywrap_tensorflow.py", line 58, in <module>
    from tensorflow.python.pywrap_tensorflow_internal import *
  File "/usr/local/lib/python3.5/dist-packages/tensorflow/python/pywrap_tensorflow_internal.py", line 28, in <module>
    _pywrap_tensorflow_internal = swig_import_helper()
  File "/usr/local/lib/python3.5/dist-packages/tensorflow/python/pywrap_tensorflow_internal.py", line 24, in swig_import_helper
    _mod = imp.load_module('_pywrap_tensorflow_internal', fp, pathname, description)
  File "/usr/lib/python3.5/imp.py", line 242, in load_module
    return load_dynamic(name, filename, file)
  File "/usr/lib/python3.5/imp.py", line 342, in load_dynamic
    return _load(spec)
ImportError: /usr/lib/arm-linux-gnueabihf/libstdc++.so.6: version `GLIBCXX_3.4.22' not found (required by /usr/local/lib/python3.5/dist-packages/tensorflow/python/_pywrap_tensorflow_internal.so)


Failed to load the native TensorFlow runtime.

See https://www.tensorflow.org/install/install_sources#common_installation_problems

for some common reasons and solutions.  Include the entire stack trace
above this error message when asking for help.
```
GLIBCXX_3.4.22がないことが原因。
```
strings /usr/lib/arm-linux-gnueabihf/libstdc++.so.6|grep GLIBCXX
```
でどこまでのバージョンまでインストールできているか確認できる。

追加方法は、下記でうまくいった。

```
sudo add-apt-repository ppa:ubuntu-toolchain-r/test
sudo apt-get update
sudo apt-get install gcc-6 g++-6
```

念のため、
https://qiita.com/samacoba/items/c3291addba06ea6206c1
を参考にして動作確認を行ったが問題なく動いた。(と思う)


###参考にした記事
https://stackoverflow.com/questions/46077958/libstdc-error-glibcxx-3-4-22-not-found
https://stackoverflow.com/questions/44794111/multiple-version-of-libstdc-in-raspberry-pi-3
https://askubuntu.com/questions/746369/how-can-i-install-and-use-gcc-6-on-xenial