Function differentiate 

pub fn differentiate<F, Func>(x: F, h: F, evalfn: Func) -> Result<F, String>
where
    F: Float + FromPrimitive + Debug,
    Func: Fn(F) -> Result<F, String>,

Differentiate a function using central difference method.

Arguments

• x - Point at which to evaluate the derivative
• h - Step size for the finite difference
• eval_fn - Function that evaluates the function at a point

Returns

• Derivative of the function at x

Examples

use scirs2_core::utils::differentiate;

// Differentiate f(x) = x^2 at x = 3
let f = |x: f64| -> Result<f64, String> { Ok(x * x) };
let derivative = differentiate(3.0, 0.001, f).unwrap();

// The exact derivative is 2x = 6 at x = 3
assert!((derivative - 6.0).abs() < 1e-5);

Errors

Returns an error if the evaluation function fails at either x+h or x-h.