I am creating geometry for the use in pde toolbox. I exported the mesh of the 3D geometry from COMSOL, and I realized that the element matrix of the surface is a 3-by-Nelements matrix while the rest of the geometry is a 4-by-Nelements. I wonder how I concatenate the two matrices. I tried to put  as the 4th row for the 3-by-Nelements matrix but it did not work.
Thank you very much!