Is there any $f\in H^1(\mathbb T^n)$ such that: $$\textrm{div}(f):=\sum_{j=1}^n \partial_j f=1,$$ where $1$ stands for the constant function $x\longmapsto 1$.
Thanks.
Is there any $f\in H^1(\mathbb T^n)$ such that: $$\textrm{div}(f):=\sum_{j=1}^n \partial_j f=1,$$ where $1$ stands for the constant function $x\longmapsto 1$.
Thanks.
Well, the torus being compact, the function must have a maximum somewhere. At this point the divergence is 0.