In mathematics, preconditioning is a procedure of an application of a transformation, called the preconditioner, that conditions a given problem into a form that is more suitable for numerical solution. Preconditioning is typically related to reducing a condition number of the problem. The preconditioned problem is then usually solved by an iterative method.
Read more about Preconditioner: Preconditioning For Linear Systems, Preconditioning For Eigenvalue Problems, Preconditioning in Optimization