pub fn gradient_uniform(y: &[f64], h: f64) -> Vec<f64>Expand description
Numerical gradient with uniform spacing using 5-point stencil (O(h⁴)).
Interior points use the 5-point central difference:
g[i] = (-y[i+2] + 8*y[i+1] - 8*y[i-1] + y[i-2]) / (12*h)
Near-boundary points use appropriate forward/backward formulas.