/** Convert regular functions to {@link MultivariateDifferentiableFunction}. ...*/

public static MultivariateDifferentiableFunction toDifferentiable(final MultivariateFunction f,

final MultivariateVectorFunction gradient) {

return new MultivariateDifferentiableFunction() {

/** {@inheritDoc} */

@Override

public double value(final double[] point) { return f.value(point); }

/** {@inheritDoc} */

@Override

public DerivativeStructure value(final DerivativeStructure[] point) {

// set up the input parameters

final double[] dPoint = new double[point.length];

for (int i = 0; i < point.length; ++i) {

dPoint[i] = point[i].getValue();

if (point[i].getOrder() > 1) {

throw new NumberIsTooLargeException(point[i].getOrder(), 1, true);

}

}

// evaluate regular functions

final double v = f.value(dPoint);

final double[] dv = gradient.value(dPoint);

if (dv.length != point.length) {

// the gradient function is inconsistent

throw new DimensionMismatchException(dv.length, point.length);

}

// build the combined derivative

final int parameters = point[0].getFreeParameters();

final double[] partials = new double[point.length];

final double[] packed = new double[parameters + 1];

packed[0] = v;

final int orders[] = new int[parameters];

for (int i = 0; i < parameters; ++i) {