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Mathematic support for Strata

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/*
 * Copyright (C) 2009 - present by OpenGamma Inc. and the OpenGamma group of companies
 *
 * Please see distribution for license.
 */
package com.opengamma.strata.math.impl.linearalgebra;

import java.util.HashMap;
import java.util.Map;

import com.opengamma.strata.math.linearalgebra.Decomposition;

/**
 * Factory class for different types of decompositions.
 */
public final class DecompositionFactory {

  /** Commons LU decomposition */
  public static final String LU_COMMONS_NAME = "LU_COMMONS";
  /** Commons QR decomposition */
  public static final String QR_COMMONS_NAME = "QR_COMMONS";
  /** Commons SV decomposition */
  public static final String SV_COMMONS_NAME = "SV_COMMONS";
  /** {@link LUDecompositionCommons} */
  public static final Decomposition LU_COMMONS = new LUDecompositionCommons();
  /** {@link QRDecompositionCommons} */
  public static final Decomposition QR_COMMONS = new QRDecompositionCommons();
  /** {@link SVDecompositionCommons} */
  public static final Decomposition SV_COMMONS = new SVDecompositionCommons();
  private static final Map> STATIC_INSTANCES;
  private static final Map, String> INSTANCE_NAMES;

  static {
    STATIC_INSTANCES = new HashMap<>();
    STATIC_INSTANCES.put(LU_COMMONS_NAME, LU_COMMONS);
    STATIC_INSTANCES.put(QR_COMMONS_NAME, QR_COMMONS);
    STATIC_INSTANCES.put(SV_COMMONS_NAME, SV_COMMONS);
    INSTANCE_NAMES = new HashMap<>();
    INSTANCE_NAMES.put(LU_COMMONS.getClass(), LU_COMMONS_NAME);
    INSTANCE_NAMES.put(QR_COMMONS.getClass(), QR_COMMONS_NAME);
    INSTANCE_NAMES.put(SV_COMMONS.getClass(), SV_COMMONS_NAME);
  }

  private DecompositionFactory() {
  }

  /**
   * Given a name, returns an instance of that decomposition method.
   * 
   * @param decompositionName The name of the decomposition method
   * @return The decomposition method
   * @throws IllegalArgumentException If the decomposition name is null or there is no decomposition method of that name
   */
  public static Decomposition getDecomposition(String decompositionName) {
    Decomposition decomposition = STATIC_INSTANCES.get(decompositionName);
    if (decomposition != null) {
      return decomposition;
    }
    throw new IllegalArgumentException("Could not get decomposition " + decompositionName);
  }

  /**
   * Given a decomposition method, returns its name.
   * 
   * @param decomposition The decomposition method
   * @return The name of the decomposition method (null if not found)
   */
  public static String getDecompositionName(Decomposition decomposition) {
    if (decomposition == null) {
      return null;
    }
    return INSTANCE_NAMES.get(decomposition.getClass());
  }

}