• Charfi, Salma (Faculty of Sciences of Sfax Department of Mathematics) ;
  • Walha, Ines (Faculty of Sciences of Sfax Department of Mathematics)
  • Received : 2015.04.04
  • Published : 2016.05.31


In this paper, we investigate relative essential spectra of $2{\times}2$ block operator matrix using the Fredholm perturbation theory. Furthermore, an example for two-group transport equations is presented to illustrate the validity of the main results.


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