linearInterpolation<T> function

UnaryFunction<T> linearInterpolation<T>(DataType<T> dataType, { required Vector<T> xs, required Vector<T> ys, T? left, T? right, })

A function providing linear interpolation of a discrete monotonically increasing set of sample points xs and ys. Returns left or right, if the point is outside the data range, by default extrapolate linearly.

See https://en.wikipedia.org/wiki/Linear_interpolation.

Implementation

UnaryFunction<T> linearInterpolation<T>(
  DataType<T> dataType, {
  required Vector<T> xs,
  required Vector<T> ys,
  T? left,
  T? right,
}) {
  checkPoints(dataType, xs: xs, ys: ys, min: 1, ordered: true, unique: true);
  final add = dataType.field.add, sub = dataType.field.sub;
  final mul = dataType.field.mul, div = dataType.field.div;
  final min = xs.getUnchecked(0), max = xs.getUnchecked(xs.count - 1);
  final comparator = dataType.comparator;
  final slopes = Vector<T>.generate(
      dataType,
      xs.count - 1,
      (i) => div(sub(ys.getUnchecked(i + 1), ys.getUnchecked(i)),
          sub(xs.getUnchecked(i + 1), xs.getUnchecked(i))),
      format: VectorFormat.standard);
  return (T x) {
    if (left != null && comparator.lessThan(x, min)) {
      return left;
    } else if (right != null && comparator.greaterThan(x, max)) {
      return right;
    } else {
      final index = comparator.binarySearchLeft(xs, x).clamp(1, xs.count - 1);
      return add(
          ys.getUnchecked(index - 1),
          mul(slopes.getUnchecked(index - 1),
              sub(x, xs.getUnchecked(index - 1))));
    }
  };
}