Struct Spline 

pub struct Spline { /* private fields */ }

A cubic spline f(x) = a·(x−x_i)³ + b·(x−x_i)² + c·(x−x_i) + y_i.

One cubic piece per interval, expressed relative to that interval’s left knot; a/b/c are the per-interval coefficients and y the knot values.

Implementations

impl Spline

pub fn new(xs: Vec<f64>, ys: Vec<f64>) -> Self

Build a cubic spline with natural boundary conditions and quadratic extrapolation — salmon’s default tk::spline(xs, ys).

The construction: demand that neighbouring cubics agree in value, slope and curvature at each interior knot. That gives one equation per interior knot in the unknown second derivatives (b), the natural boundary conditions pin the two ends, and the resulting tridiagonal system is solved above. a and c then follow directly from b.

pub fn eval(&self, x: f64) -> f64

Evaluate the spline at x (interpolating, or extrapolating quadratically outside [x_0, x_{n-1}]).

The nesting ((a·h + b)·h + c)·h + y is Horner’s rule: the same polynomial with three multiplications instead of six, and better rounding behaviour.

Trait Implementations

impl Clone for Spline

fn clone(&self) -> Spline

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Spline

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for Spline

fn default() -> Spline

Returns the “default value” for a type.