Matrix defined in Appendices C and D is singular and hence expressions containing the inverse of cannot be used as such. The singularity is a consequence of the chosen organization of the matrix-vector differential equation in these appendices. The field vector contains nine stress components of which only six are independent. By removing the three redundant stress components from and reorganizing the matrix-vector equation accordingly, we obtain a matrix that is invertible. The redefined matrices and in Appendices C and D obey symmetry relations (9) and (13) in the body of the paper. Hence, the unified reciprocity theorems (12) and (14) are valid for the modified matrix-vector differential equation in these appendices. Explicit expressions for the modified matrices and vectors can be found at http://geodus1.ta.tudelft.nl/PrivatePages/C.P.A.Wapenaar/4_Journals/J.Appl.Mech/AppM_04.pdfhttp://geodus1.ta.tudelft.nl/PrivatePages/C.P.A.Wapenaar/4_Journals/J.Appl.Mech/AppM_04.pdf.
We take this opportunity to indicate some printing errors in the paper. The tildes below and in Eq. (1) should be removed. Circumflexes should be added above all vectors and in Eqs. (10) and (11). A right-bracket ] should be inserted after the first at the right-hand side of Eq. (10). Right-parentheses ) should be inserted after at the left-hand side of Eq. (11) and after the first at the right-hand side of Eq. (11).
We thank Stefan Stijlen for bringing the singularity of matrix to our attention.