Estimates for the combined effect of boundary
approximation and numerical integration on the approximation of
(simple) eigenvalues and eigenvectors of 4th order
eigenvalue problems with variable/constant coefficients
in convex domains with curved boundary by an isoparametric mixed
finite element method, which,
in the particular case of bending problems of
aniso-/ortho-/isotropic plates with variable/constant
thickness, gives a simultaneous approximation to bending moment
tensor field $\Psi= (\psi_{ij})_{1 \le i,j \le 2}$ and
displacement field `u', have been developed.