# geqslib - Grant's Equation Solver Library
Geqslib defines several functions for evaluating expressions and solving equations given as strings. The crate provides both single and multiple-variable implementations of the Newton-Raphson root-finding algorithm and provides them for use in other scenarios where expressions may be better represented by a closure than a string.
Most of the provided functions, however, are focused on evaluating expressions or equations as strings:
# Example
```rust
use geqslib::solve_equation_from_str;
let (var, soln) = solve_equation_from_str("x + 4 = 12", 0.0001, 10).unwrap();
assert_eq!(var, "x");
assert!((soln - 8.0).abs() < 0.001);
```
Geqslib also provides a `SystemBuilder` struct for properly constraining a system of equations for later solving.
# Example
```rust
use geqslib::system::{System, SystemBuilder};
use geqslib::shunting::new_context;
let mut ctx = new_context();
// Build up the system:
let mut builder = SystemBuilder::new("x + y = 9", ctx).unwrap();
builder.try_constrain_with("x - y = 4");
// Convert to a constrained system
let mut sys = builder
.build_system()
.expect("Failed to constrain system...");
// Specify guess value and domain for variables if desired
sys.specify_variable("x", 6.5, 0.0, 7.0);
// Specify tolerance and iteration limit, then solve!
let soln = sys.solve(0.0001, 10)
.expect("Failed to find a solution...");
// Solution is x = 6.5, y = 2.5
assert!((6.5 - soln["x"]).abs() < 0.001);
assert!((2.5 - soln["y"]).abs() < 0.001);
```