AbstractAlfriend1999.java
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package org.orekit.ssa.collision.shorttermencounter.probability.twod;
import org.hipparchus.CalculusFieldElement;
import org.hipparchus.linear.BlockFieldMatrix;
import org.hipparchus.linear.BlockRealMatrix;
import org.hipparchus.linear.FieldLUDecomposition;
import org.hipparchus.linear.FieldMatrix;
import org.hipparchus.linear.LUDecomposition;
import org.hipparchus.linear.RealMatrix;
import org.hipparchus.util.MathArrays;
import org.orekit.ssa.metrics.FieldProbabilityOfCollision;
import org.orekit.ssa.metrics.ProbabilityOfCollision;
/**
* Abstract class for Alfriend1999 normal and maximised methods as they share lots of similarities.
*
* @author Vincent Cucchietti
* @since 12.0
*/
public abstract class AbstractAlfriend1999 extends AbstractShortTermEncounter2DPOCMethod {
/**
* Default constructor.
*
* @param name name of the method
*/
protected AbstractAlfriend1999(final String name) {
super(name);
}
/** {@inheritDoc} */
@Override
public ProbabilityOfCollision compute(final double xm, final double ym, final double sigmaX, final double sigmaY,
final double radius) {
// Reconstruct necessary values from inputs
final double squaredMahalanobisDistance =
ShortTermEncounter2DDefinition.computeSquaredMahalanobisDistance(xm, ym, sigmaX, sigmaY);
// Compute covariance matrix determinant
final double covarianceMatrixDeterminant = computeCovarianceMatrixDeterminant(sigmaX, sigmaY);
// Compute probability of collision
final double value = computeValue(radius, squaredMahalanobisDistance, covarianceMatrixDeterminant);
return new ProbabilityOfCollision(value, getName(), this.isAMaximumProbabilityOfCollisionMethod());
}
/** {@inheritDoc} */
@Override
public <T extends CalculusFieldElement<T>> FieldProbabilityOfCollision<T> compute(final T xm, final T ym, final T sigmaX,
final T sigmaY,
final T radius) {
// Reconstruct necessary values from inputs
final T squaredMahalanobisDistance =
FieldShortTermEncounter2DDefinition.computeSquaredMahalanobisDistance(xm, ym, sigmaX, sigmaY);
// Compute covariance matrix determinant
final T covarianceMatrixDeterminant = computeCovarianceMatrixDeterminant(sigmaX, sigmaY);
// Compute probability of collision
final T value = computeValue(radius, squaredMahalanobisDistance, covarianceMatrixDeterminant);
return new FieldProbabilityOfCollision<>(value, getName(), this.isAMaximumProbabilityOfCollisionMethod());
}
/**
* Compute the covariance matrix determinant.
*
* @param sigmaX square root of the x-axis eigen value of the diagonalized combined covariance matrix projected onto the
* collision plane (m)
* @param sigmaY square root of the y-axis eigen value of the diagonalized combined covariance matrix projected onto the
* collision plane (m)
*
* @return covariance matrix determinant
*/
private double computeCovarianceMatrixDeterminant(final double sigmaX, final double sigmaY) {
// Rebuild covariance matrix
final RealMatrix covarianceMatrix = new BlockRealMatrix(new double[][] {
{ sigmaX * sigmaX, 0 },
{ 0, sigmaY * sigmaY }
});
// Compute determinant
return new LUDecomposition(covarianceMatrix).getDeterminant();
}
/**
* Compute the covariance matrix determinant.
*
* @param sigmaX square root of the x-axis eigen value of the diagonalized combined covariance matrix projected onto the
* collision plane (m)
* @param sigmaY square root of the y-axis eigen value of the diagonalized combined covariance matrix projected onto the
* collision plane (m)
* @param <T> type of the field elements
*
* @return covariance matrix determinant
*/
private <T extends CalculusFieldElement<T>> T computeCovarianceMatrixDeterminant(final T sigmaX, final T sigmaY) {
// Rebuild covariance matrix
final T[][] covarianceMatrixData = MathArrays.buildArray(sigmaX.getField(), 2, 2);
covarianceMatrixData[0][0] = sigmaX.multiply(sigmaX);
covarianceMatrixData[1][1] = sigmaY.multiply(sigmaY);
final FieldMatrix<T> covarianceMatrix = new BlockFieldMatrix<>(covarianceMatrixData);
// Compute determinant
return new FieldLUDecomposition<>(covarianceMatrix).getDeterminant();
}
/**
* Compute the value of the probability of collision.
*
* @param radius sum of primary and secondary collision object equivalent sphere radii (m)
* @param squaredMahalanobisDistance squared Mahalanobis distance
* @param covarianceMatrixDeterminant covariance matrix determinant
*
* @return value of the probability of collision
*/
abstract double computeValue(double radius, double squaredMahalanobisDistance, double covarianceMatrixDeterminant);
/**
* Compute the value of the probability of collision.
*
* @param radius sum of primary and secondary collision object equivalent sphere radii (m)
* @param squaredMahalanobisDistance squared Mahalanobis distance
* @param covarianceMatrixDeterminant covariance matrix determinant
* @param <T> type of the field elements
*
* @return value of the probability of collision
*/
abstract <T extends CalculusFieldElement<T>> T computeValue(T radius, T squaredMahalanobisDistance,
T covarianceMatrixDeterminant);
}