public void integrate()

in commons-math-legacy/src/main/java/org/apache/commons/math4/legacy/ode/nonstiff/AdamsMoultonIntegrator.java [209:337]
87 lines of code
12 McCabe index (conditional complexity)

    public void integrate(final ExpandableStatefulODE equations,final double t)
        throws NumberIsTooSmallException, DimensionMismatchException,
               MaxCountExceededException, NoBracketingException {

        sanityChecks(equations, t);
        setEquations(equations);
        final boolean forward = t > equations.getTime();

        // initialize working arrays
        final double[] y0   = equations.getCompleteState();
        final double[] y    = y0.clone();
        final double[] yDot = new double[y.length];
        final double[] yTmp = new double[y.length];
        final double[] predictedScaled = new double[y.length];
        Array2DRowRealMatrix nordsieckTmp = null;

        // set up two interpolators sharing the integrator arrays
        final NordsieckStepInterpolator interpolator = new NordsieckStepInterpolator();
        interpolator.reinitialize(y, forward,
                                  equations.getPrimaryMapper(), equations.getSecondaryMappers());

        // set up integration control objects
        initIntegration(equations.getTime(), y0, t);

        // compute the initial Nordsieck vector using the configured starter integrator
        start(equations.getTime(), y, t);
        interpolator.reinitialize(stepStart, stepSize, scaled, nordsieck);
        interpolator.storeTime(stepStart);

        double hNew = stepSize;
        interpolator.rescale(hNew);

        isLastStep = false;
        do {

            double error = 10;
            while (error >= 1.0) {

                stepSize = hNew;

                // predict a first estimate of the state at step end (P in the PECE sequence)
                final double stepEnd = stepStart + stepSize;
                interpolator.setInterpolatedTime(stepEnd);
                final ExpandableStatefulODE expandable = getExpandable();
                final EquationsMapper primary = expandable.getPrimaryMapper();
                primary.insertEquationData(interpolator.getInterpolatedState(), yTmp);
                int index = 0;
                for (final EquationsMapper secondary : expandable.getSecondaryMappers()) {
                    secondary.insertEquationData(interpolator.getInterpolatedSecondaryState(index), yTmp);
                    ++index;
                }

                // evaluate a first estimate of the derivative (first E in the PECE sequence)
                computeDerivatives(stepEnd, yTmp, yDot);

                // update Nordsieck vector
                for (int j = 0; j < y0.length; ++j) {
                    predictedScaled[j] = stepSize * yDot[j];
                }
                nordsieckTmp = updateHighOrderDerivativesPhase1(nordsieck);
                updateHighOrderDerivativesPhase2(scaled, predictedScaled, nordsieckTmp);

                // apply correction (C in the PECE sequence)
                error = nordsieckTmp.walkInOptimizedOrder(new Corrector(y, predictedScaled, yTmp));

                if (error >= 1.0) {
                    // reject the step and attempt to reduce error by stepsize control
                    final double factor = computeStepGrowShrinkFactor(error);
                    hNew = filterStep(stepSize * factor, forward, false);
                    interpolator.rescale(hNew);
                }
            }

            // evaluate a final estimate of the derivative (second E in the PECE sequence)
            final double stepEnd = stepStart + stepSize;
            computeDerivatives(stepEnd, yTmp, yDot);

            // update Nordsieck vector
            final double[] correctedScaled = new double[y0.length];
            for (int j = 0; j < y0.length; ++j) {
                correctedScaled[j] = stepSize * yDot[j];
            }
            updateHighOrderDerivativesPhase2(predictedScaled, correctedScaled, nordsieckTmp);

            // discrete events handling
            System.arraycopy(yTmp, 0, y, 0, y.length);
            interpolator.reinitialize(stepEnd, stepSize, correctedScaled, nordsieckTmp);
            interpolator.storeTime(stepStart);
            interpolator.shift();
            interpolator.storeTime(stepEnd);
            stepStart = acceptStep(interpolator, y, yDot, t);
            scaled    = correctedScaled;
            nordsieck = nordsieckTmp;

            if (!isLastStep) {

                // prepare next step
                interpolator.storeTime(stepStart);

                if (resetOccurred) {
                    // some events handler has triggered changes that
                    // invalidate the derivatives, we need to restart from scratch
                    start(stepStart, y, t);
                    interpolator.reinitialize(stepStart, stepSize, scaled, nordsieck);
                }

                // stepsize control for next step
                final double  factor     = computeStepGrowShrinkFactor(error);
                final double  scaledH    = stepSize * factor;
                final double  nextT      = stepStart + scaledH;
                final boolean nextIsLast = forward ? (nextT >= t) : (nextT <= t);
                hNew = filterStep(scaledH, forward, nextIsLast);

                final double  filteredNextT      = stepStart + hNew;
                final boolean filteredNextIsLast = forward ? (filteredNextT >= t) : (filteredNextT <= t);
                if (filteredNextIsLast) {
                    hNew = t - stepStart;
                }

                interpolator.rescale(hNew);
            }
        } while (!isLastStep);

        // dispatch results
        equations.setTime(stepStart);
        equations.setCompleteState(y);

        resetInternalState();
    }