# Expressions Expressions is a feature, which allows constructing lazily or immediately calculated parametric mathematical expressions. The potential use-cases for it (so far) are following: * lazy evaluation (in general simple lambda is better, but there are some border cases); * automatic differentiation in single-dimension and in multiple dimensions; * generation of mathematical syntax trees with subsequent code generation for other languages; * symbolic computations, especially differentiation (and some other actions with `kmath-symja` integration with Symja's `IExpr`—integration, simplification, and more); * visualization with `kmath-jupyter`. The workhorse of this API is `Expression` interface, which exposes single `operator fun invoke(arguments: Map): T` method. `ExpressionAlgebra` is used to generate expressions and introduce variables. Currently there are two implementations: * Generic `ExpressionField` in `kmath-core` which allows construction of custom lazy expressions * Auto-differentiation expression in `kmath-commons` module allows using full power of `DerivativeStructure` from commons-math. **TODO: add example**