Axis labels for graphs?

I'd like to use gnuplot 2d graphs in my LaTeX document. I need to have a LaTeX expression in the title of y-axis, for example $\langle \psi | \psi \rangle$ rotated vertically and centered at the axis.

What would be the best way to do it?

Can I use LaTeX expressions in gnuplot? I know one can use Greek symbols in gnuplot.

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2nd comment in this forum post helps old.nabble.com/… – kirill_igum Nov 1 '10 at 3:54

I see now after more careful reading of your question that you are interested in rotated and centered text. In that case, if you have a recent version of gnuplot, you can try the new tikz terminal. There is an example available here.
I did not notice that you want to rotate the labels, I just concentrated on the part of your question where you ask about using LaTeX expressions in gnuplot. You can rotate latex boxes using the graphicx package, but using the tikz terminal will give you more options. To produce a png image, you can start with pdf from pdflatex, and convert it to png. – Jan Hlavacek Nov 1 '10 at 4:01