jetson nanoでscikit learnインストール時にエラー（error: library mach has Fortran sources but no Fortran compiler found）

jetson nanoでscikit learnインストール時にエラー

$ pip3 install scikit-learn
...
  error: library mach has Fortran sources but no Fortran compiler found
    ----------------------------------------
    ERROR: Failed building wheel for scipy
  Failed to build scipy
  ERROR: Could not build wheels for scipy which use PEP 517 and cannot be installed directly
  ----------------------------------------
ERROR: Command errored out with exit status 1: /usr/bin/python3 /home/jetson/.local/lib/python3.6/site-packages/pip install --ignore-installed --no-user --prefix /tmp/pip-build-env-jkfyvtro/overlay --no-warn-script-location --no-binary :none: --only-binary :none: -i https://pypi.org/simple -- setuptools wheel 'Cython>=0.28.5' 'numpy==1.13.3; python_version=='"'"'3.6'"'"' and platform_system!='"'"'AIX'"'"' and platform_python_implementation == '"'"'CPython'"'"'' 'numpy==1.14.0; python_version=='"'"'3.6'"'"' and platform_system!='"'"'AIX'"'"' and platform_python_implementation != '"'"'CPython'"'"'' 'numpy==1.14.5; python_version=='"'"'3.7'"'"' and platform_system!='"'"'AIX'"'"'' 'numpy==1.17.3; python_version>='"'"'3.8'"'"' and platform_system!='"'"'AIX'"'"'' 'numpy==1.16.0; python_version=='"'"'3.6'"'"' and platform_system=='"'"'AIX'"'"'' 'numpy==1.16.0; python_version=='"'"'3.7'"'"' and platform_system=='"'"'AIX'"'"'' 'numpy==1.17.3; python_version>='"'"'3.8'"'"' and platform_system=='"'"'AIX'"'"'' 'scipy>=0.19.1' Check the logs for full command output.

以下で解決
（なんでscikit-learn install時にfortranがいるの？）

sudo apt install -y gfortran

参考

pip-failing-to-build-wheels-for-scipy
errors-during-install-sklearn