System of linear equations
In mathematics, the theory of linear systems is a branch of linear algebra, a subject which is fundamental to modern mathematics. Computer algorithms for finding the solutions are an important part of numerical linear algebra, and such methods play a prominent role in engineering, physics, chemistry, computer science, and economics. A system of non-linear equations can often be approximated by a linear system (see linearization), a helpful technique when making a mathematical model, computer model, or computer simulation of a relatively complex system.  For complex systems, there are many equations and many variables, not just two or three. In many cases, the number of equations and variables in the system are the same.  In some cases, there are more variables than equations, and the solution will be a range of different values rather than one exact solution.