Press Ctrl-V and the Tab character where you see [TAB]:
$ sed 's/[[:space:]]\{1,\}/[TAB]/g' in.mtx > out.mtx
Press Ctrl-V and the Tab character where you see [TAB]:
$ sed 's/[[:space:]]\{1,\}/[TAB]/g' in.mtx > out.mtx
This assumes Homebrew is installed and that it installs Graphviz 2.40.1:
$ brew install graphviz $ git clone https://github.com/pygraphviz/pygraphviz.git $ cd pygraphviz $ sudo python setup.py install --user --include-path=/usr/local/Cellar/graphviz/2.40.1/include --library-path=/usr/local/Cellar/graphviz/2.40.1/lib