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+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.commons.math3.ode.nonstiff;
+
+import org.apache.commons.math3.Field;
+import org.apache.commons.math3.RealFieldElement;
+import org.apache.commons.math3.ode.FieldEquationsMapper;
+import org.apache.commons.math3.ode.FieldODEStateAndDerivative;
+
+/**
+ * This class implements a linear interpolator for step.
+ *
+ * <p>This interpolator computes dense output inside the last
+ * step computed. The interpolation equation is consistent with the
+ * integration scheme :
+ * <ul>
+ * <li>Using reference point at step start:<br>
+ * y(t<sub>n</sub> + &theta; h) = y (t<sub>n</sub>) + &theta; h y'
+ * </li>
+ * <li>Using reference point at step end:<br>
+ * y(t<sub>n</sub> + &theta; h) = y (t<sub>n</sub> + h) - (1-&theta;) h y'
+ * </li>
+ * </ul>
+ * </p>
+ *
+ * where &theta; belongs to [0 ; 1] and where y' is the evaluation of
+ * the derivatives already computed during the step.</p>
+ *
+ * @see EulerFieldIntegrator
+ * @param <T> the type of the field elements
+ * @since 3.6
+ */
+
+class EulerFieldStepInterpolator<T extends RealFieldElement<T>>
+ extends RungeKuttaFieldStepInterpolator<T> {
+
+ /** Simple constructor.
+ * @param field field to which the time and state vector elements belong
+ * @param forward integration direction indicator
+ * @param yDotK slopes at the intermediate points
+ * @param globalPreviousState start of the global step
+ * @param globalCurrentState end of the global step
+ * @param softPreviousState start of the restricted step
+ * @param softCurrentState end of the restricted step
+ * @param mapper equations mapper for the all equations
+ */
+ EulerFieldStepInterpolator(final Field<T> field, final boolean forward,
+ final T[][] yDotK,
+ final FieldODEStateAndDerivative<T> globalPreviousState,
+ final FieldODEStateAndDerivative<T> globalCurrentState,
+ final FieldODEStateAndDerivative<T> softPreviousState,
+ final FieldODEStateAndDerivative<T> softCurrentState,
+ final FieldEquationsMapper<T> mapper) {
+ super(field, forward, yDotK,
+ globalPreviousState, globalCurrentState, softPreviousState, softCurrentState,
+ mapper);
+ }
+
+ /** {@inheritDoc} */
+ @Override
+ protected EulerFieldStepInterpolator<T> create(final Field<T> newField, final boolean newForward, final T[][] newYDotK,
+ final FieldODEStateAndDerivative<T> newGlobalPreviousState,
+ final FieldODEStateAndDerivative<T> newGlobalCurrentState,
+ final FieldODEStateAndDerivative<T> newSoftPreviousState,
+ final FieldODEStateAndDerivative<T> newSoftCurrentState,
+ final FieldEquationsMapper<T> newMapper) {
+ return new EulerFieldStepInterpolator<T>(newField, newForward, newYDotK,
+ newGlobalPreviousState, newGlobalCurrentState,
+ newSoftPreviousState, newSoftCurrentState,
+ newMapper);
+ }
+
+ /** {@inheritDoc} */
+ @SuppressWarnings("unchecked")
+ @Override
+ protected FieldODEStateAndDerivative<T> computeInterpolatedStateAndDerivatives(final FieldEquationsMapper<T> mapper,
+ final T time, final T theta,
+ final T thetaH, final T oneMinusThetaH) {
+ final T[] interpolatedState;
+ final T[] interpolatedDerivatives;
+ if (getGlobalPreviousState() != null && theta.getReal() <= 0.5) {
+ interpolatedState = previousStateLinearCombination(thetaH);
+ interpolatedDerivatives = derivativeLinearCombination(time.getField().getOne());
+ } else {
+ interpolatedState = currentStateLinearCombination(oneMinusThetaH.negate());
+ interpolatedDerivatives = derivativeLinearCombination(time.getField().getOne());
+ }
+
+ return new FieldODEStateAndDerivative<T>(time, interpolatedState, interpolatedDerivatives);
+
+ }
+
+}