/**
* Computes the value of the gradient at {@code x}. The components of the gradient vector are
* the partial derivatives of the function with respect to each of the <em>parameters</em>
* (amplitude, angular frequency and phase).
*
* @param x Value at which the gradient must be computed.
* @param param Values of amplitude, angular frequency and phase.
* @return the gradient vector at {@code x}.
* @throws NullArgumentException if {@code param} is {@code null}.
* @throws DimensionMismatchException if the size of {@code param} is not 3.
*/
public double[] gradient(double x, double... param) {
validateParameters(param);
final double amplitude = param[0];
final double omega = param[1];
final double phase = param[2];
final double xTimesOmegaPlusPhase = omega * x + phase;
final double a = HarmonicOscillator.value(xTimesOmegaPlusPhase, 1);
final double p = -amplitude * FastMath.sin(xTimesOmegaPlusPhase);
final double w = p * x;
return new double[] {a, w, p};
}
/**
* Computes the value of the harmonic oscillator at {@code x}.
*
* @param x Value for which the function must be computed.
* @param param Values of norm, mean and standard deviation.
* @return the value of the function.
* @throws NullArgumentException if {@code param} is {@code null}.
* @throws DimensionMismatchException if the size of {@code param} is not 3.
*/
public double value(double x, double... param) {
validateParameters(param);
return HarmonicOscillator.value(x * param[1] + param[2], param[0]);
}
