Published online by Cambridge University Press: 21 September 2023
We make some remarks on the Euler–Lagrange equation of energy functional $I(u)=\int _\Omega f(\det Du)\,{\rm d}x,$
 where $f\in C^1(\mathbb {R}).$
 For certain weak solutions $u$
 we show that the function $f'(\det Du)$
 must be a constant over the domain $\Omega$
 and thus, when $f$
 is convex, all such solutions are an energy minimizer of $I(u).$
 However, other weak solutions exist such that $f'(\det Du)$
 is not constant on $\Omega.$
 We also prove some results concerning the homeomorphism solutions, non-quasimonotonicity and radial solutions, and finally we prove some stability results and discuss some related questions concerning certain approximate solutions in the 2-Dimensional cases.