A library to parse and evaluate mathematical expressions with inbuilt elementwise vector operations
Get Started
$ dotnet add package VectorExpressionEngineReadme
VectorExpressionEngine
This library can be used to formulate mathematical expressions and evaluate them. The library can handle abitrary types, and it supports working with arrays/vectors in an elementwise maner (similar to MATLAB). This makes working with array data, like time series, very fast.
The library is extendable, custom types can be handled and new functions and constants can be crated easily.
Usage
To use the library, first a context is required. This context allows the resolving of functions and variables, as well as storage of new variables. The library comes with two context implementations - ReflectionContext and ScopedContext.
public class MathLibrary
{
// This provides a function called "sin" that simply calls the Math.Sin function
[Expression("sin")]
public double Sin(double x) => Math.Sin(x);
// This provides a constant called "pi"
[Expression("pi")]
public double Pi => Math.PI;
}
...
// this is the expression to evaluate
var expression = "sin(45 * pi/180)";
// this will parse the given expression, returning a node object
var node = Parser.ParseSingle(expression);
// setup a library
var library = new MathLibrary();
// setup a context with the custom library
var reflectionContext = new ReflectionContext(library);
// evaluate the node to return a result
var result = node.Eval(reflectionContext); // result will be a double with value 1/sqrt(2) = 0.7071
The ReflectionContext is a read-only context. If variables are to be stored, a different context is required - e.g. the ScopedContext:
// setup a ScopedContext using the previously defined ReflectionContext:
var scopedContext = new ScopedContext(reflectionContext);
// this time multiple expressions are chained, separated by ';'
var expressionChain = "x=2; y=x*4; y+x";
// this will parse the expressions into an array of nodes
var nodes = Parser.Parse(expressionChain);
// this will evaluate all nodes, and return an array of results
var results = nodes.Select(node => node.Eval(scopedContext)).ToArray();
var finalResult = results.Last(); // this will contain the result of the calculation 2*4+2 = 10
