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Diffstat (limited to 'src/main/java/org/apache/commons/math3/ode/nonstiff/MidpointFieldStepInterpolator.java')
| -rw-r--r-- | src/main/java/org/apache/commons/math3/ode/nonstiff/MidpointFieldStepInterpolator.java | 118 |
1 files changed, 118 insertions, 0 deletions
diff --git a/src/main/java/org/apache/commons/math3/ode/nonstiff/MidpointFieldStepInterpolator.java b/src/main/java/org/apache/commons/math3/ode/nonstiff/MidpointFieldStepInterpolator.java new file mode 100644 index 0000000..911e3b2 --- /dev/null +++ b/src/main/java/org/apache/commons/math3/ode/nonstiff/MidpointFieldStepInterpolator.java @@ -0,0 +1,118 @@ +/* + * 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 step interpolator for second order + * Runge-Kutta integrator. + * + * <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> + θ h) = y (t<sub>n</sub>) + θ h [(1 - θ) y'<sub>1</sub> + θ y'<sub>2</sub>] + * </li> + * <li>Using reference point at step end:<br> + * y(t<sub>n</sub> + θ h) = y (t<sub>n</sub> + h) + (1-θ) h [θ y'<sub>1</sub> - (1+θ) y'<sub>2</sub>] + * </li> + * </ul> + * </p> + * + * where θ belongs to [0 ; 1] and where y'<sub>1</sub> and y'<sub>2</sub> are the two + * evaluations of the derivatives already computed during the + * step.</p> + * + * @see MidpointFieldIntegrator + * @param <T> the type of the field elements + * @since 3.6 + */ + +class MidpointFieldStepInterpolator<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 + */ + MidpointFieldStepInterpolator(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 MidpointFieldStepInterpolator<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 MidpointFieldStepInterpolator<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 coeffDot2 = theta.multiply(2); + final T coeffDot1 = time.getField().getOne().subtract(coeffDot2); + final T[] interpolatedState; + final T[] interpolatedDerivatives; + + if (getGlobalPreviousState() != null && theta.getReal() <= 0.5) { + final T coeff1 = theta.multiply(oneMinusThetaH); + final T coeff2 = theta.multiply(thetaH); + interpolatedState = previousStateLinearCombination(coeff1, coeff2); + interpolatedDerivatives = derivativeLinearCombination(coeffDot1, coeffDot2); + } else { + final T coeff1 = oneMinusThetaH.multiply(theta); + final T coeff2 = oneMinusThetaH.multiply(theta.add(1)).negate(); + interpolatedState = currentStateLinearCombination(coeff1, coeff2); + interpolatedDerivatives = derivativeLinearCombination(coeffDot1, coeffDot2); + } + + return new FieldODEStateAndDerivative<T>(time, interpolatedState, interpolatedDerivatives); + + } + +} |