我正在试图安装并使用Graphviz，并且我急需在我的节点标签中使用下标。不幸的是，在浏览了无数关于类似问题的帖子后，似乎我符合所有提出的解决方案，但仍然无法正常工作。以下是我的代码：
digraph G{
execute [label=<ex<SUB>2</SUB>>];
main -> parse -> execute;
main -> init;
main -> cleanup;
init -> make_string;
main -> printf;
}
同时运行以下命令：
$ dot -Tps:cairo -v test.gv -o out.ps
输出内容为：
> dot - graphviz version 2.26.3 (20100126.1600)
Activated plugin library: libgvplugin_pango.so.6
Using textlayout: textlayout:cairo
Activated plugin library: libgvplugin_dot_layout.so.6
Using layout: dot:dot_layout
Using render: cairo:cairo
Using device: ps:cairo:cairo
The plugin configuration file:
/usr/lib/graphviz/config6
was successfully loaded.
render : cairo dot fig gd map ps svg tk vml vrml xdot
layout : circo dot fdp neato nop nop1 nop2 osage patchwork sfdp twopi
textlayout : textlayout
device : canon cmap cmapx cmapx_np dot eps fig gd gd2 gif gv imap imap_np ismap jpe jpeg jpg pdf plain plain-ext png ps ps2 svg svgz tk vml vmlz vrml wbmp x11 xdot xlib
loadimage : (lib) eps gd gd2 gif jpe jpeg jpg png ps svg
Error: Unknown HTML element <SUB> on line 1
fontname: "Times-Roman" resolved to: (ps:pango Times Roman,) (PangoCairoFcFont) "DejaVu Sans 14"
in label of node execute
network simplex: 7 nodes 6 edges maxiter=2147483647 balance=1
network simplex: 7 nodes 6 edges 0 iter 0.00 sec
mincross: pass 0 iter 0 trying 0 cur_cross 0 best_cross 0
mincross G: 0 crossings, 0.00 secs.
network simplex: 13 nodes 16 edges maxiter=2147483647 balance=2
network simplex: 13 nodes 16 edges 1 iter 0.00 sec
routesplines: 6 edges, 18 boxes 0.00 sec
Using render: cairo:cairo
Using device: ps:cairo:cairo
我不太熟悉cairo或svg渲染，并且我不确定它是与graphviz捆绑在一起还是完全是一个单独的库。我使用Ubuntu 12，通过apt-get安装了graphviz。非常感谢任何帮助。谢谢。