Balayage
In potential theory, a mathematical discipline, balayage (from French: balayage "scanning, sweeping") is a method devised by Henri Poincaré for reconstructing an harmonic function in a domain from its values on the boundary of the domain. In modern terms, the balayage operator maps a measure μ {\displaystyle \mu } on a closed domain D {\displaystyle D} to a measure ν {\displaystyle \nu } on the boundary ∂ D {\displaystyle \partial D} , so that the Newtonian potentials of μ {\displaystyle \mu } and ν {\displaystyle \nu } coincide outside D ¯ {\displaystyle {\bar {D}}} .