This is a very basic tool to visualize cluster algebras, as described
by e.g. Marsh in [1]. I'll not go over the theory here.

The easiest way to see how this works is to run

    ./cluster-algebra-visualize 7_a.txt

which shows one pair of faces of a n=7 simplex fitted with the quiver
described in [2]. To perform the flip described in [2], we can mutate
as follows:

    m 10 4 0 2 a 1a
    m 11 5 1 9 19 23 f 3 b 1b
    m 12 6 8 18 4 0 2 a 22 e c 1c
    m 13 7 17 5 1 9 f 3 b 21 d 1d
    m 14 16 6 8 0 2 e c 20 1e
    m 15 7 1 3 d 1f

And the result is, as predicted, the quiver which would be attached to
the opposite pair of faces (7_b.txt).

Caveats:

  o No good error handling at all.

  o The display is a haphazard mixture of unicode and ASCII (you'll
    see what that means). I completely blame the current state of
    monospaced unicode-aware fonts at the moment, which render unicode
    arrows as double-width in contradiction to wcwidth(3). Unicode
    arrows are therefore unsuitable for extensive use in a TUI at the
    moment.

  o Arrows with multiplicity greater than 1 are not obvious: they are
    simply drawn in reverse. There is no way to see what the
    multiplicity is.

  o Arrows which overlap other arrows are not drawn intelligently. It
    may be difficult to find out where an arrow starts or ends.

  o Points are labelled in hexadecimal, so when more than 16 points
    are onscreen, during point selection the labels might overwrite
    other data.

  o To delete an arrow, add another arrow going the other way.

  o I wrote this over the course of a weekend and never really
    expected anyone else to use it. This documentation is mostly for
    my own sake.

References:

[1] Robert Marsh, Lecture notes on cluster algebras, European
    Mathematical Society, Zürich, 2013.

[2] Vladimir Fock and Alexander Goncharov, Moduli spaces of local
    systems and higher Teichmüller theory, Publications Mathématiques
    de l’Institut des Hautes Études Scientifiques 103, no. 1, 1–211,
    DOI 10.1007/s10240-006-0039-4. Preprint at
    <http://arxiv.org/abs/math/0311149v4>