@Test
public void firstDerivativeTest() {
double a = 1.0;
double b = 1.5;
double c = -0.5;
double[] x = new double[] {0., 2., 5.};
int n = x.length;
double[] y = new double[n];
for (int i = 0; i < n; i++) {
y[i] = a + b * x[i] + c * x[i] * x[i];
}
Interpolator1D interpolator = new NaturalCubicSplineInterpolator1D();
Interpolator1DDataBundle db = interpolator.getDataBundle(x, y);
Double grad = interpolator.firstDerivative(db, x[n - 1]);
Function1D<Double, Double> func = interpolator.getFunction(db);
ScalarFirstOrderDifferentiator diff = new ScalarFirstOrderDifferentiator();
Function1D<Double, Boolean> domain =
new Function1D<Double, Boolean>() {
@Override
public Boolean evaluate(Double x) {
return x <= 5.0;
}
};
Function1D<Double, Double> gradFunc = diff.differentiate(func, domain);
assertEquals(gradFunc.evaluate(x[n - 1]), grad, 1e-8);
}
@Override
public double firstDerivative(final Interpolator1DDataBundle data, final Double value) {
return _transform.inverseTransformGradient(_base.interpolate(data, value))
* _base.firstDerivative(data, value);
}
@Override
public double firstDerivative(
Interpolator1DDataBundle data, Double value, Interpolator1D interpolator) {
JodaBeanUtils.notNull(data, "data");
return interpolator.firstDerivative(data, value);
}
