001/*
002 * Units of Measurement Reference Implementation
003 * Copyright (c) 2005-2017, Jean-Marie Dautelle, Werner Keil, V2COM.
004 *
005 * All rights reserved.
006 *
007 * Redistribution and use in source and binary forms, with or without modification,
008 * are permitted provided that the following conditions are met:
009 *
010 * 1. Redistributions of source code must retain the above copyright notice,
011 *    this list of conditions and the following disclaimer.
012 *
013 * 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions
014 *    and the following disclaimer in the documentation and/or other materials provided with the distribution.
015 *
016 * 3. Neither the name of JSR-363 nor the names of its contributors may be used to endorse or promote products
017 *    derived from this software without specific prior written permission.
018 *
019 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
020 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
021 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
022 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
023 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
024 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
025 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
026 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
027 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
028 * EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
029 */
030package tec.units.ri.spi;
031
032import java.util.Map;
033
034import javax.measure.Dimension;
035import javax.measure.UnitConverter;
036
037import tec.units.ri.AbstractConverter;
038import tec.units.ri.quantity.QuantityDimension;
039
040/**
041 * <p>
042 * This class represents the physical model used for dimensional analysis.
043 * </p>
044 *
045 * <p>
046 * In principle, dimensions of physical quantities could be defined as "fundamental" (such as momentum or energy or electric current) making such
047 * quantities uncommensurate (not comparable). Modern physics has cast doubt on the very existence of incompatible fundamental dimensions of physical
048 * quantities. For example, most physicists do not recognize temperature, {@link QuantityDimension#TEMPERATURE ?}, as a fundamental dimension since it
049 * essentially expresses the energy per particle per degree of freedom, which can be expressed in terms of energy (or mass, length, and time). To
050 * support, such model the method {@link #getConverter} may returns a non-null value for distinct dimensions.
051 * </p>
052 * 
053 * <p>
054 * The default model is {@link StandardModel Standard}. Applications may use one of the predefined model or create their own. <code>
055 *     DimensionalModel relativistic = new DimensionalModel() {
056 *         public Dimension getFundamentalDimension(Dimension dimension) {
057 *             if (dimension.equals(QuantityDimension.LENGTH)) return QuantityDimension.TIME; // Consider length derived from time.
058 *                 return super.getDimension(dimension); // Returns product of fundamental dimension.
059 *             }
060 *             public UnitConverter getDimensionalTransform(Dimension dimension) {
061 *                 if (dimension.equals(QuantityDimension.LENGTH)) return new RationalConverter(1, 299792458); // Converter (1/C) from LENGTH SI unit (m) to TIME SI unit (s).
062 *                 return super.getDimensionalTransform(dimension);
063 *             }
064 *     };
065 *     try {
066 *         DimensionalModel.setCurrent(relativistic); // Current thread use the relativistic model.
067 *         Units.KILOGRAM.getConverterToAny(Units.JOULE); // Allowed.
068 *         ...
069 *     } finally {
070 *         cleanup();
071 *     }
072 *     </code>
073 * </p>
074 * 
075 * @see <a href="http://en.wikipedia.org/wiki/Dimensional_analysis">Wikipedia: Dimensional Analysis</a>
076 * @author <a href="mailto:jean-marie@dautelle.com">Jean-Marie Dautelle</a>
077 * @author <a href="mailto:units@catmedia.us">Werner Keil</a>
078 * @version 1.0, $Date: 2016-10-06 $
079 */
080public abstract class DimensionalModel {
081
082  /**
083   * Holds the current model.
084   */
085  private static DimensionalModel currentModel = new StandardModel();
086
087  /**
088   * Returns the current dimensional model (by default an instance of {@link StandardModel}).
089   *
090   * @return the current physical model.
091   */
092  public static DimensionalModel current() {
093    return currentModel;
094  }
095
096  /**
097   * Sets the current dimensional model
098   *
099   * @param model
100   *          the new current model.
101   * @see #current
102   */
103  protected static void setCurrent(DimensionalModel model) {
104    currentModel = model;
105  }
106
107  /**
108   * Default constructor (allows for derivation).
109   */
110  protected DimensionalModel() {
111  }
112
113  /**
114   * Returns the fundamental dimension for the one specified. If the specified dimension is a dimensional product, the dimensional product of its
115   * fundamental dimensions is returned. Physical quantities are considered commensurate only if their fundamental dimensions are equals using the
116   * current physics model.
117   *
118   * @param dimension
119   *          the dimension for which the fundamental dimension is returned.
120   * @return <code>this</code> or a rational product of fundamental dimension.
121   */
122  public Dimension getFundamentalDimension(Dimension dimension) {
123    Map<? extends Dimension, Integer> dimensions = dimension.getBaseDimensions();
124    if (dimensions == null)
125      return dimension; // Fundamental dimension.
126    // Dimensional Product.
127    Dimension fundamentalProduct = QuantityDimension.NONE;
128    for (Map.Entry<? extends Dimension, Integer> e : dimensions.entrySet()) {
129      fundamentalProduct = fundamentalProduct.multiply(this.getFundamentalDimension(e.getKey())).pow(e.getValue());
130    }
131    return fundamentalProduct;
132  }
133
134  /**
135   * Returns the dimensional transform of the specified dimension. If the specified dimension is a fundamental dimension or a product of fundamental
136   * dimensions the identity converter is returned; otherwise the converter from the system unit (SI) of the specified dimension to the system unit
137   * (SI) of its fundamental dimension is returned.
138   *
139   * @param dimension
140   *          the dimension for which the dimensional transform is returned.
141   * @return the dimensional transform (identity for fundamental dimensions).
142   * @throws UnsupportedOperationException
143   *           if an unsupported transform is attemted.
144   */
145  public UnitConverter getDimensionalTransform(Dimension dimension) {
146    Map<? extends Dimension, Integer> dimensions = dimension.getBaseDimensions();
147    if (dimensions == null)
148      return AbstractConverter.IDENTITY; // Fundamental dimension.
149    // Dimensional Product.
150    UnitConverter toFundamental = AbstractConverter.IDENTITY;
151    for (Map.Entry<? extends Dimension, Integer> e : dimensions.entrySet()) {
152      UnitConverter cvtr = this.getDimensionalTransform(e.getKey());
153      if (!(cvtr.isLinear()))
154        throw new UnsupportedOperationException("Non-linear dimensional transform");
155      int pow = e.getValue();
156      if (pow < 0) { // Negative power.
157        pow = -pow;
158        cvtr = cvtr.inverse();
159      }
160      for (int j = 0; j < pow; j++) {
161        toFundamental = toFundamental.concatenate(cvtr);
162      }
163    }
164    return toFundamental;
165  }
166}