21. Thus, the power spectral density function is a set of Dirac delta functions . 22. Where \ delta ( \ bold r ) is the 3-dimensional delta function . 23. Setting gives the associated nascent delta function . 24. The delta function in this incidence algebra similarly corresponds to the formal power series 1. 25. Under certain conditions, the Kronecker delta can arise from sampling a Dirac delta function . 26. But as the Fourier transform of a delta function is a constant, we can write 27. This is simply a flat plane that contains a negative-valued Dirac delta function . 28. For a proof, see e . g . the article on the surface delta function . 29. It also represents a nascent delta function in the sense that in the distribution sense as. 30. Applying Fourier inversion to these delta functions , we obtain the elementary solutions we picked earlier.
