private <T extends RealFieldElement<T>> RungeKuttaFieldStepInterpolator<T> setUpInterpolator(
final Field<T> field,
final FirstOrderFieldDifferentialEquations<T> eqn,
final double t0,
final double[] y0,
final double t1) {
// get the Butcher arrays from the field integrator
FieldButcherArrayProvider<T> provider = createButcherArrayProvider(field);
T[][] a = provider.getA();
T[] b = provider.getB();
T[] c = provider.getC();
// store initial state
T t = field.getZero().add(t0);
T[] fieldY = MathArrays.buildArray(field, eqn.getDimension());
T[][] fieldYDotK = MathArrays.buildArray(field, b.length, -1);
for (int i = 0; i < y0.length; ++i) {
fieldY[i] = field.getZero().add(y0[i]);
}
fieldYDotK[0] = eqn.computeDerivatives(t, fieldY);
FieldODEStateAndDerivative<T> s0 = new FieldODEStateAndDerivative<T>(t, fieldY, fieldYDotK[0]);
// perform one integration step, in order to get consistent derivatives
T h = field.getZero().add(t1 - t0);
for (int k = 0; k < a.length; ++k) {
for (int i = 0; i < y0.length; ++i) {
fieldY[i] = field.getZero().add(y0[i]);
for (int s = 0; s <= k; ++s) {
fieldY[i] = fieldY[i].add(h.multiply(a[k][s].multiply(fieldYDotK[s][i])));
}
}
fieldYDotK[k + 1] = eqn.computeDerivatives(h.multiply(c[k]).add(t0), fieldY);
}
// store state at step end
t = field.getZero().add(t1);
for (int i = 0; i < y0.length; ++i) {
fieldY[i] = field.getZero().add(y0[i]);
for (int s = 0; s < b.length; ++s) {
fieldY[i] = fieldY[i].add(h.multiply(b[s].multiply(fieldYDotK[s][i])));
}
}
FieldODEStateAndDerivative<T> s1 =
new FieldODEStateAndDerivative<T>(t, fieldY, eqn.computeDerivatives(t, fieldY));
return createInterpolator(
field, t1 > t0, fieldYDotK, s0, s1, s0, s1, new FieldExpandableODE<T>(eqn).getMapper());
}
/**
* Evaluate the value of the polynomial.
*
* @param tc date offset in Julian centuries
* @return value of the polynomial
*/
public T value(final T tc) {
T p = tc.getField().getZero();
for (int i = coefficients.length - 1; i >= 0; --i) {
p = p.multiply(tc).add(coefficients[i]);
}
return p;
}
// unchecked cast {@code (T)amount.with(MonetaryOperator)} is
// safe, if the operator is implemented as specified by this JSR.
@SuppressWarnings("unchecked")
@Override
public <T extends MonetaryAmount> T apply(T amount) {
return (T) amount.multiply(permilValue);
}
