Example 216
Heterosis plate bending element: Q8 for geometry & w,
Q9 for deflection w, and in plane rotations theta_1, theta_2
Order DOF as w, theta_1, theta_2 at each node (but no w_9)
theta_1 = w,x and theta_2 = w,y

DATA_SET 01
Heterosis sq plate with center point load, Buchanan Ex 7.18
4 Q9 elements, full model
Exact center deflection is 0.3502 inch (found 3.5015E-01)

DATA_SET 02
Heterosis sq plate with center point load, Buchanan Ex 7.18
4 Q9 elements, one-quarter symmetry model
Exact center deflection is 0.3502 inch (found 3.5343E-01)