Comment on the paper "Improving Poor Man's Kramers-Kronig analysis and Kramers-Kronig constrained variational analysis".

Abstract The title paper [Spectrochim. Acta A 213 (2019): 391-396] reports an improvement of the ”Poor Man’s Kramers-Kronig analysis” and of the ”Kramers-Kronig constrained variational analysis” thanks to an ad hoc modification of some analytical formulas existing in the literature. This ad hoc modification is not based on mathematical grounds. In this comment we show that no ad hoc modification is required but a correction of the analytical formula used by the authors of the title paper [Spectrochim. Acta A 213 (2019): 391-396].