We study the set f’(X) = f’(x): x ∈ X when f:X → ℝ is a differentiable bump. We first prove that for any C²-smooth bump f: ℝ² → ℝ the range of the derivative of f must be the closure of its interior. Next we show that if X is an infinite-dimensional separable Banach space with a -smooth bump b:X → ℝ such that is finite, then any connected open subset of X* containing 0 is the range of the derivative of a -smooth bump. We also study the finite-dimensional case which is quite different. Finally, we show that in infinite-dimensional separable smooth Banach spaces, every analytic subset of X* which satisfies a natural linkage condition is the range of the derivative of a C¹-smooth bump. We then find an analogue of this condition in the finite-dimensional case
@article{bwmeta1.element.bwnjournal-article-doi-10_4064-sm153-1-6, author = {T. Gaspari}, title = {On the range of the derivative of a real-valued function with bounded support}, journal = {Studia Mathematica}, volume = {151}, year = {2002}, pages = {81-99}, zbl = {1033.46036}, language = {en}, url = {http://dml.mathdoc.fr/item/bwmeta1.element.bwnjournal-article-doi-10_4064-sm153-1-6} }
T. Gaspari. On the range of the derivative of a real-valued function with bounded support. Studia Mathematica, Tome 151 (2002) pp. 81-99. http://gdmltest.u-ga.fr/item/bwmeta1.element.bwnjournal-article-doi-10_4064-sm153-1-6/