Anti-de Sitter space bell. It might be described as being the "opposite" of the surface of a sphere, which has a positive curvature. General relativity is a theory of the nature of time, space and gravity in which gravity is a curvature of space and time that results from the presence of matter or energy. Energy and mass are equivalent (as expressed in the equation "E" = "mc"), and space and time can be translated into equivalent units based on the speed of light ("c" in the "E" = "mc" equation). A common analogy involves the way that a dip in a flat
Helmholtz equation the original complex amplitude "A": The Fresnel diffraction integral is an exact solution to the paraxial Helmholtz equation. There is even a subject named "Helmholtz optics" based on the equation, named in honour of Helmholtz. The inhomogeneous Helmholtz equation is the equation where "ƒ" : R → C is a function with compact support, and "n" = 1, 2, 3. This equation is very similar to the screened Poisson equation, and would be identical if the plus sign (in front of the "k" term) is switched to a minus sign. In order to solve this equation uniquely, one needs to