What are approximations?

Some articles on approximations, approximation:

Local-density Approximation
... Local-density approximations (LDA) are a class of approximations to the exchange-correlation (XC) energy functional in density functional theory (DFT) that depend solely ... Many approaches can yield local approximations to the XC energy ... However, overwhelmingly successful local approximations are those that have been derived from the homogeneous electron gas (HEG) model ...
Richardson Extrapolation - General Formula
... Let A(h) be an approximation of A that depends on a positive step size h with an error formula of the form where the ai are unknown constants and the ki are known ... can be solved for A to give By this process, we have achieved a better approximation of A by subtracting the largest term in the error which was O(hk0) ... process can be repeated to remove more error terms to get even better approximations ...
Square Root Of 5 - Diophantine Approximations
... Hurwitz's theorem in Diophantine approximations states that every irrational number x can be approximated by infinitely many rational numbers m/n in lowest terms in such a ...
Super-logarithm - Approximations - Quadratic Approximation
... The quadratic approximation to the super-logarithm is which is a piecewise-defined function with a quadratic "critical piece" ... The first author to publish this approximation was Andrew Robbins in this paper ...