Upsilon/apps/regression/model/cubic_model.cpp

#include "cubic_model.h"
#include <math.h>
#include <assert.h>

namespace Regression {

double CubicModel::evaluate(double * modelCoefficients, double x) const {
  double a = modelCoefficients[0];
  double b = modelCoefficients[1];
  double c = modelCoefficients[2];
  double d = modelCoefficients[3];
  return a*x*x*x+b*x*x+c*x+d;
}

double CubicModel::partialDerivate(double * modelCoefficients, int derivateCoefficientIndex, double x) const {
  if (derivateCoefficientIndex == 0) {
    // Derivate: x^3
    return x*x*x;
  }
  if (derivateCoefficientIndex == 1) {
    // Derivate: x^2
    return x*x;
  }
  if (derivateCoefficientIndex == 2) {
    // Derivate: x
    return x;
  }
  if (derivateCoefficientIndex == 3) {
    // Derivate: 1
    return 1;
  }
  assert(false);
  return 0.0;
}

}