Calculate the order parameter for Umbrella Sampling of dislocation nucleation.
Not a general purpose utility.

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Reference: Proc. Natl. Acad. Sci. <a href="http://www.stanford.edu/~caiwei/papers.html#59">
108, 5174 (2011)</a>, J. Mater. Res. <a href="http://www.stanford.edu/~caiwei/papers.html#63">
26, 2335 (2011)</a>.

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For details, ask Seunghwa Ryu.

