Calculate the reduced stiffness matrix for a ply.
A 
matrix is a 3x3 matrix representing the plane stress (or reduced) stiffness matrix for a particular material ply in a laminate, expressed in the global coordinate system. Once the matrix is computed, the global stress components {σ} in the ply can be computed by multiplying the matrix by the global strain components {ε} in the ply, i.e., 
.
Once a laminate is defined in the Laminate tab, the matrix can be calculated for each ply by clicking the Calculate button in the Q-Bars tab. The results are displayed in the results window of the Q-Bars tab. After the matrices are computed and displayed, click Export to write the results to a *.csv file compatible with Microsoft Excel.
