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Sep 29, 2010 at 14:47 comment added John Craighead Scott, Thanks for the insights & context. My initial post should have mentioned my interest as homogeneous elastic deformation (F depending only on time, not position). By "represented", I mean representing these deformations as some combination of (sub)groups with physical meaning (i.e. pure stretch, shear, etc.) like done with rigid body motion (i.e. SO(3) X R^3). Thanks, John.
Sep 29, 2010 at 14:11 comment added S. Carnahan I think the answer is that it depends on what you mean by "represented". Often there is a volume-conservation constraint, so you are stuck with the subgroup $SL_2(\mathbf{R})$. The decompositions you mention are well-known in the theory of Lie groups, e.g., $F=RU$ is called Iwasawa decomposition. I should note that shears may have negative entries off the diagonal.
Sep 29, 2010 at 14:07 history edited S. Carnahan CC BY-SA 2.5
Lots of minor adjustments
Sep 29, 2010 at 13:45 history asked John Craighead CC BY-SA 2.5