Generalized functions are continuous linear functionals defined on certain “well-behaved” function spaces. The smaller the “well-behaved” function space, the larger the space (the dual space) formed by the continuous linear functionals on it, thus including many “singular” functions. Generalized functions originated from some phenomena observed by physicists and engineers in the 1920 and 1930s, especially when the British physicist P. A. Dirac (1902–1984), who shared the 1933 Nobel Prize in Physics with E. Schrödinger (1887–1961), proposed the Delta function ( \(\delta \) function, Dirac function) while studying quantum mechanics