2 citations · 2 across the 2 of their papers we have counts for
2 papers
math.SP2020★ 2 cited
Courant-sharp eigenvalues of compact flat surfaces: Klein bottles and cylinders
Pierre Bérard, Bernard Helffer, Rola Kiwan
The question of determining for which eigenvalues there exists an eigenfunction which has the same number of nodal domains as the label of the associated eigenvalue (Courant-sharp…
math.SP2019
Non-boundedness of the number of super level domains of eigenfunctions
Pierre Bérard, Philippe Charron, Bernard Helffer
Generalizing Courant's nodal domain theorem, the "Extended Courant property" is the statement that a linear combination of the first eigenfunctions has at most nodal domain…