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Hello!
First at all: sory my bad english

i use latex beamer to make a presentation.
i draw with tikz and foreach one graph:
\foreach \pos/\name in {{(0,2)/S2}, {(0,4)/S1}, {(4,3)/A}}
\node (\name) at \pos [] {$\name$};

\foreach \source/ \dest /\weight in {S1/A/5, S2/A/8}
\draw[->] (\source) to ...