I am using signalflowdiagram from here: http://www.texample.net/tikz/examples/signal-flow-building-blocks/. Then I installed it in my texmf-local folder. The tree looks like this:

/usr/local/texlive/texmf-local

tex

├── latex

│   ├── local

│   ├── signalflowlibrary

│   │   ├── macros.sty

│   │   ├── signalflowdiagram.sty

│   │   ├── tikzlibrarysignalflowarrows.code.tex

│   │   ├── tikzlibrarysignalflowblocks.code.tex

│   │   ├── tikzlibrarysignalflowdiagram.code.tex

│   │   └── tikzlibrarysignalflowoperators.code.tex

...

After copying the necessary files to the tree as shown above, I ran $ mktexlsr to make sure LaTeX can find the new custom package.

I can confirm that it works properly because this code:

documentclass[crop,tikz]{standalone}

usepackage{signalflowdiagram}



begin{document}

  begin{signalflow}{Block diagram}

    begin{scope}

      node[input] (in) {$R(s)$};

      node[filter] (plant) [right from=in] {$G(s)$};

      path[r>] (in) -- (plant);

    end{scope}

  end{signalflow}

end{document}

produces this picture:

The problem

Now I want to position the nodes using matrix. First, I will show that I can get matrix to work, nothing fancy:

documentclass[crop,tikz]{standalone}

usepackage{tikz}

%usepackage{signalflowdiagram}

usetikzlibrary{matrix}



begin{document}

  begin{tikzpicture}

  matrix (m) [matrix of nodes]

  {%

    1 & 2 & 3 \

    4 & 5 & 6 \

  };

  end{tikzpicture}

end{document}

So I get this:

This time, I want to use the predefined blocks in signalflowdiagram, so I uncomment the line that says usepackage{signalflowdiagram}. My code now looks like this. Notice the use of signalflow and scope environments as shown in the first example above.

documentclass[crop,tikz]{standalone}

usepackage{tikz}

usepackage{signalflowdiagram}

usetikzlibrary{matrix}



begin{document}

  begin{signalflow}{Block diagram}

    begin{scope}

      matrix (m) [matrix of nodes]

      {%

        1 & 2 & 3 \

        4 & 5 & 6 \

      };

    end{scope}

  end{signalflow}

end{document}

Nothing appears :o I have not even started using the predefined blocks in signalflowdiagram.

Even using an ordinary tikzpicture draws nothing:

documentclass[crop,tikz]{standalone}
usepackage{tikz}
usepackage{signalflowdiagram}
usetikzlibrary{matrix}

begin{document}
begin{tikzpicture}
matrix (m) [matrix of nodes]
{%
1 & 2 & 3
4 & 5 & 6
};
end{tikzpicture}
end{document}

The common denominator

As long as usepackage{signalflowdiagram} is present, all matrix disappear.

Is there a way to get signalflowdiagram to work with matrix? I did try hacking into the signalflowdiagram code files, disabling definition of new environments, etc., to no avail.