Ergonomics

ChebyshevSharp v0.8.0 adds a suite of ergonomic accessors and constructor sugar features across all four interpolant classes. This page summarizes the new surface.

Descriptors

A free-form text label you can attach to any interpolant. Survives save/load.

var approx = new ChebyshevApproximation(
    (p, _) => p[0] + p[1],
    numDimensions: 2,
    domain: new[] { new[] { -1.0, 1.0 }, new[] { -1.0, 1.0 } },
    nNodes: new[] { 5, 5 });
approx.Build();
approx.SetDescriptor("Black-Scholes 2D, vol=20%");

string? label = approx.GetDescriptor();

Additional Data

Pass calibration parameters through every f(point, data) call during build:

double scale = 0.25;
var approx = new ChebyshevApproximation(
    (p, data) => p[0] + (double)data! * p[1],
    numDimensions: 2,
    domain: new[] { new[] { -1.0, 1.0 }, new[] { -1.0, 1.0 } },
    nNodes: new[] { 5, 5 },
    additionalData: scale);
approx.Build();

object? stored = approx.GetAdditionalData();

additionalData is not serialized in JSON or .pcb files.

ChebyshevTT stores additionalData for introspection but doesn't thread it (its function signature is Func<double[], double>).

Derivative ID Registry

Stable session-local int per derivative-orders tuple:

int delta = approx.GetDerivativeId(new[] { 1, 0 });
int gamma = approx.GetDerivativeId(new[] { 2, 0 });

double d = approx.Eval(point, delta);
double g = approx.Eval(point, gamma);

The registry is per-instance and does persist across Save/Load on all supported interpolant classes.

Introspection

bool ready = approx.IsConstructionFinished();
string how = approx.GetConstructorType();
int[] ns = approx.GetUsedNs();
int maxOrder = approx.GetMaxDerivativeOrder();
double? thr = approx.GetErrorThreshold();    // Approx/Spline only
double[][]? sp = approx.GetSpecialPoints();   // Approx/Spline only
int n = approx.GetNumEvaluationPoints();
double[] pts = approx.GetEvaluationPoints();  // length = n × ndim, row-major

Cloning

ChebyshevApproximation clone = approx.Clone();
// clone.Function == null; clone is independent of source

Deferred Build (Approximation + Spline)

var deferred = new ChebyshevApproximation(
    (_, _) => throw new InvalidOperationException("not used"),
    numDimensions: 2,
    domain: new[] { new[] { -1.0, 1.0 }, new[] { -1.0, 1.0 } },
    nNodes: new[] { 5, 5 },
    deferBuild: true);
// IsConstructionFinished() == false; Eval/Save throw.

double[] precomputed = new double[25];
deferred.SetOriginalFunctionValues(precomputed);
// IsConstructionFinished() == true; constructor type is "from_values".

Typed Domain/Ns/SpecialPoints Records

var d = new Domain(new[] { new[] { -1.0, 1.0 }, new[] { -1.0, 1.0 } });
double[][] back = d;          // implicit Domain -> double[][]
Domain again = back;          // implicit double[][] -> Domain