Herz–Schur multiplier

The Herz–Schur multiplier is a concept from functional analysis, particularly in the context of operator theory and harmonic analysis. It is named after mathematicians Heinrich Herz and Hugo Schur, who contributed to the development of multiplier theories associated with function spaces. In general terms, a Herz–Schur multiplier pertains to the action of a bounded linear operator on certain function spaces, often involving Fourier transforms or Fourier series.