However, it can be approximated to within a constant approximation ratio using semidefinite programming. Therefore, the Fourier Transform is numerically approximated using the discrete Fourier transform formula 21. Unit response can be approximated mathematically by a convolution operation. Linear deformations of elastic materials can be approximated as adiabatic. True photorealism occurs when the rendering equation is closely approximated or fully implemented. The Inverse Kinematics problem can also be approximated using heuristic methods. Instead, solutions can be approximated using numerical methods. For nonlinear systems, this interaction is often approximated by linear functions. Similarly, factorials can be approximated by summing the logarithms of the terms. It is commonly approximated using the Mohr-Coulomb equation. They can only be approximated by decimal numerals, denoting rounded or truncated real numbers. The cost is frequently defined as a statistic whose value can only be approximated. The weighted variant can also be approximated as well. Nevertheless, the "Q"-function can be approximated arbitrarily well as formula 70 becomes larger and larger. Gases under certain conditions can be approximated as incompressible.