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Mathematical optimization

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Mathematical optimization is the science of selecting the best possible element from a set of available alternatives. It is a vital part of applied mathematics used to make decisions based on specific criteria.

Max paraboloid
Max paraboloid

In practice, this means finding the highest or lowest value of a mathematical rule. This rule is called an objective function. Depending on the goal, the process is called maximization or minimization. If the goal is to find the lowest value, it is often called a cost function or loss function. If the goal is to find the highest value, it is called a utility or fitness function. Optimization helps experts in computer science, engineering, and economics solve complex problems.

To solve these problems, mathematicians work within a defined search space. This space contains all the possible choices, known as candidate solutions or feasible solutions. A solution is only considered feasible if it satisfies certain rules called constraints. These constraints can be equalities or inequalities that limit the choices. When a candidate solution perfectly satisfies the objective function by being the best, it is called an optimal solution. In many fields, such as physics, optimization is used to find energy minimization. This means finding the state where a system has the lowest possible energy.

Optimization problems are divided into two primary categories based on their variables. The first type is discrete optimization. In this category, the variables are countable, such as integers, permutations, or graphs. The second type is continuous optimization. This involves finding optimal arguments from a continuous set, such as any real number on a line. Problems can also be classified by their shape or structure. For example, convex problems are often easier to solve than nonconvex problems. In a convex minimization problem, any local minimum is also the global minimum. However, nonconvex problems may have many local minima that are not the absolute best.

A local minimum is an element that is better than all nearby elements. A global minimum is the absolute best element among every feasible choice in the entire set.

Nelder-Mead Simionescu
Nelder-Mead Simionescu

Many modern computer solvers struggle to distinguish between these two types of solutions. They may stop at a local minimum and treat it as the final answer. Global optimization is a specific branch of mathematics dedicated to this challenge. It develops deterministic algorithms that can guarantee they will find the true global solution in a finite amount of time.

The history of optimization is filled with significant mathematical discoveries. Early mathematicians like Fermat and Lagrange developed calculus-based formulas to identify optimal points. Later, Newton and Gauss proposed iterative methods to move step-by-step toward an optimum. In 1939, Leonid Kantorovich introduced important theories related to linear programming. In 1947, George B. Dantzig published the Simplex algorithm. Dantzig developed this while studying logistics and training schedules for the United States military. Around this same time, John von Neumann and other researchers worked on the theoretical aspects of linear programming, such as the theory of duality.

There are many specialized subfields within optimization that address different mathematical structures. Linear programming is a common type of convex programming where the objective function and constraints are linear. Integer programming is more difficult because it requires some variables to be whole numbers. Nonlinear programming handles cases where the functions or constraints are not straight lines. Other advanced methods include semidefinite programming, which uses semidefinite matrices, and stochastic programming, which accounts for random variables. Some techniques, known as heuristics, are used to find approximate solutions for very complicated problems when a perfect answer is too hard to find.

Optimization connects to many different scientific and technical systems. In machine learning, it is used to evaluate the quality of data models by minimizing error. In the field of artificial intelligence, constraint satisfaction is used for automated reasoning. Scientists also use the calculus of variations to find the best way to achieve a goal, such as finding a surface with the least possible area. Optimal control theory and dynamic programming are used to make decisions over time. By turning complex choices into mathematical models, optimization provides a clear path to the best possible results in a changing world.

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