EvalExpr-JIT

A high-performance mathematical expression evaluator with JIT compilation and automatic differentiation support. Builds on top of evalexpr and Cranelift.

Features

• 🚀 JIT compilation for fast expression evaluation
• 📊 Automatic differentiation (up to any order)
• 🔢 Support for multiple variables with consistent ordering
• 🧮 Higher-order partial derivatives
• 📐 Jacobian matrix computation
• 🔄 Batch evaluation of equation systems

This crate is still under development and the API is subject to change.

Installation

Install the crate from crates.io:

cargo add evalexpr-jit

or add this to your Cargo.toml:

[dependencies]
evalexpr-jit = "0.1.2"  # Replace with actual version

Quick Start

Single Equation

The Equation struct provides a simple way to evaluate mathematical expressions and compute their derivatives. Variables are automatically detected from the expression and ordered alphabetically.

use evalexpr_jit::Equation;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Create a single equation
    let eq = Equation::new("2*x + y^2".to_string())?;
    
    // Evaluate at point (x=1, y=2)
    let result = eq.eval(&[1.0, 2.0])?;
    assert_eq!(result, 6.0); // 2*1 + 2^2 = 6
    
    // Compute gradient (vector of partial derivatives)
    let gradient = eq.gradient(&[1.0, 2.0])?;
    assert_eq!(gradient, vec![2.0, 4.0]); // [∂/∂x, ∂/∂y] = [2, 2y]
    
    // Compute Hessian matrix (matrix of second derivatives)
    let hessian = eq.hessian(&[1.0, 2.0])?;
    assert_eq!(hessian, vec![
        vec![0.0, 0.0], // [∂²/∂x², ∂²/∂x∂y]
        vec![0.0, 2.0], // [∂²/∂y∂x, ∂²/∂y²]
    ]);
    
    Ok(())
}

System of Equations

The EquationSystem struct allows you to evaluate multiple equations simultaneously, sharing variables across equations for efficient computation. Variables are automatically collected from all equations and consistently ordered.

use evalexpr_jit::system::EquationSystem;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Create a system of equations
    let system = EquationSystem::new(vec![
        "2*x + y".to_string(),   // first equation
        "x^2 + z".to_string(),   // second equation
    ])?;
    
    // Variables are automatically sorted (x, y, z)
    // Input values must be provided in the same order
    let results = system.eval(&[1.0, 2.0, 3.0])?;
    assert_eq!(results, vec![
        4.0,  // eq1: 2*1 + 2 = 4
        4.0   // eq2: 1^2 + 3 = 4
    ]); 
    
    // Get the sorted variable names to ensure correct input ordering
    println!("Variables: {:?}", system.sorted_variables); // ["x", "y", "z"]
    
    Ok(())
}

Advanced Usage

Single Equation Derivatives

The Equation struct provides multiple ways to compute derivatives, from simple partial derivatives to higher-order mixed derivatives:

use evalexpr_jit::Equation;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let eq = Equation::new("x^2 * y^2".to_string())?;

    // Get first-order partial derivative
    let dx = eq.derivative("x")?;
    let result = dx(&[2.0, 3.0]);
    assert_eq!(result, 36.0); // d/dx[x^2*y^2] = 2x*y^2 = 2*2*3^2

    // Compute higher-order mixed derivative
    let dxdy = eq.derive_wrt(&["x", "y"])?;
    let result = dxdy(&[2.0, 3.0]);
    assert_eq!(result, 12.0); // d²/dxdy[x^2*y^2] = 4xy
    
    Ok(())
}

System Derivatives and Jacobian

The EquationSystem struct provides tools for analyzing the derivatives of multiple equations simultaneously:

use evalexpr_jit::system::EquationSystem;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let system = EquationSystem::new(vec![
        "x^2*y".to_string(),   // f1
        "x*y^2".to_string(),   // f2
    ])?;

    // Compute Jacobian matrix at point (2,3)
    let jacobian = system.jacobian(&[2.0, 3.0])?;

    // Jacobian matrix:
    // [∂f1/∂x  ∂f1/∂y] = [12.0  4.0]   // derivatives of f1
    // [∂f2/∂x  ∂f2/∂y] = [9.0   12.0]  // derivatives of f2
    assert_eq!(jacobian[0], vec![12.0, 4.0]);  // derivatives of f1
    assert_eq!(jacobian[1], vec![9.0, 12.0]);  // derivatives of f2

    // Compute higher-order derivatives of the system
    let d2 = system.derive_wrt(&["x", "y"])?;
    let results = d2(&[2.0, 3.0]);
    assert_eq!(results, vec![
        4.0,  // d²/dxdy[x^2*y] = 2x
        6.0   // d²/dxdy[x*y^2] = 2y
    ]);

    Ok(())
}

Notes on Parameters and Variables

When working with expressions that contain both parameters and independent variables, you can use derive_wrt_stack to compute derivatives with respect to parameters only. This is particularly useful for parameter estimation and optimization problems.

use evalexpr_jit::Equation;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Expression with parameters (a, b) and variables (x, y)
    let eq = Equation::new("a*x^2 + b*y^2".to_string())?;
    
    // Returns a JITFunction that computes the gradient of the 
    // equation with respect to the parameters only
    let param_gradient = eq.derive_wrt_stack(&["a", "b"])?;
    
    // Values provided in alphabetical order: [a, b, x, y]
    let result = param_gradient(&[2.0, 3.0, 1.0, 2.0]);
    assert_eq!(result, vec![1.0, 4.0]); // [∂/∂a = x^2, ∂/∂b = y^2]
    
    Ok(())
}

Note that variables are always sorted alphabetically when providing input values, if no specific order is provided. In the example above, the order is [a, b, x, y]. You can check the ordering using eq.sorted_variables. If you want to provide a specific order, you can use from_var_map and provide a map of variable names to indices:

let eq = Equation::from_var_map(vec!["a*x^2 + b*y^2".to_string()], &["a", "b", "x", "y"])?;

API Reference

Equation

The basic struct for single equation evaluation:

• new(equation: String) -> Result<Self, EquationError>
• eval(&self, values: &[f64]) -> Result<f64, EquationError>
• gradient(&self, values: &[f64]) -> Result<Vec<f64>, EquationError>
• hessian(&self, values: &[f64]) -> Result<Vec<Vec<f64>>, EquationError>
• derivative(&self, variable: &str) -> Result<JITFunction, EquationError>
• derive_wrt(&self, variables: &[&str]) -> Result<JITFunction, EquationError>
• derive_wrt_stack(&self, variables: &[&str]) -> Result<JITFunction, EquationError>

EquationSystem

For evaluating systems of equations:

• new(expressions: Vec<String>) -> Result<Self, EquationError>
• from_var_map(expressions: Vec<String>, variable_map: &HashMap<String, u32>) -> Result<Self, EquationError>
• eval(&self, inputs: &[f64]) -> Result<Vec<f64>, EquationError>
• gradient(&self, inputs: &[f64], variable: &str) -> Result<Vec<f64>, EquationError>
• jacobian(&self, inputs: &[f64]) -> Result<Vec<Vec<f64>>, EquationError>
• derive_wrt(&self, variables: &[&str]) -> Result<CombinedJITFunction, EquationError>

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.