[Getdp] Shear in D1

[Brian Wilfley]

Hello,

I've been successfully using the D1 operator to do stress-strain problems.

My question is: is the third component of D1: CompZ[ {D1 u}] the
"engineering strain"?  That is, is it the sum of the crossed partials,
or the average of the crossed partials:

dv    du
--  + ---
dx    dy

or:

1  dv    du
--  --- + ---
2  dx   dy

I ask because I presume this affects the normalization of the C_m
matrix of elastic coefficients.

Thanks very much.

Brian