/*
    * 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.math4.legacy.optim.linear;
  
  import org.apache.commons.math4.legacy.linear.ArrayRealVector;
  import org.apache.commons.math4.legacy.linear.RealVector;
  
  /**
   * A linear constraint for a linear optimization problem.
   * <p>
   * A linear constraint has one of the forms:
   * <ul>
   *   <li>c<sub>1</sub>x<sub>1</sub> + ... c<sub>n</sub>x<sub>n</sub> = v</li>
   *   <li>c<sub>1</sub>x<sub>1</sub> + ... c<sub>n</sub>x<sub>n</sub> &lt;= v</li>
   *   <li>c<sub>1</sub>x<sub>1</sub> + ... c<sub>n</sub>x<sub>n</sub> &gt;= v</li>
   *   <li>l<sub>1</sub>x<sub>1</sub> + ... l<sub>n</sub>x<sub>n</sub> + l<sub>cst</sub> =
   *       r<sub>1</sub>x<sub>1</sub> + ... r<sub>n</sub>x<sub>n</sub> + r<sub>cst</sub></li>
   *   <li>l<sub>1</sub>x<sub>1</sub> + ... l<sub>n</sub>x<sub>n</sub> + l<sub>cst</sub> &lt;=
   *       r<sub>1</sub>x<sub>1</sub> + ... r<sub>n</sub>x<sub>n</sub> + r<sub>cst</sub></li>
   *   <li>l<sub>1</sub>x<sub>1</sub> + ... l<sub>n</sub>x<sub>n</sub> + l<sub>cst</sub> &gt;=
   *       r<sub>1</sub>x<sub>1</sub> + ... r<sub>n</sub>x<sub>n</sub> + r<sub>cst</sub></li>
   * </ul>
   * The c<sub>i</sub>, l<sub>i</sub> or r<sub>i</sub> are the coefficients of the constraints, the x<sub>i</sub>
   * are the coordinates of the current point and v is the value of the constraint.
   *
   * @since 2.0
   */
  public class LinearConstraint {
      /** Coefficients of the constraint (left hand side). */
      private final RealVector coefficients;
      /** Relationship between left and right hand sides {@code (=, <=, >=)}. */
      private final Relationship relationship;
      /** Value of the constraint (right hand side). */
      private final double value;
  
      /**
       * Build a constraint involving a single linear equation.
       * <p>
       * A linear constraint with a single linear equation has one of the forms:
       * <ul>
       *   <li>c<sub>1</sub>x<sub>1</sub> + ... c<sub>n</sub>x<sub>n</sub> = v</li>
       *   <li>c<sub>1</sub>x<sub>1</sub> + ... c<sub>n</sub>x<sub>n</sub> &lt;= v</li>
       *   <li>c<sub>1</sub>x<sub>1</sub> + ... c<sub>n</sub>x<sub>n</sub> &gt;= v</li>
       * </ul>
       *
       * @param coefficients The coefficients of the constraint (left hand side)
       * @param relationship The type of (in)equality used in the constraint
       * @param value The value of the constraint (right hand side)
       */
      public LinearConstraint(final double[] coefficients,
                              final Relationship relationship,
                              final double value) {
          this(new ArrayRealVector(coefficients), relationship, value);
      }
  
      /**
       * Build a constraint involving a single linear equation.
       * <p>
       * A linear constraint with a single linear equation has one of the forms:
       * <ul>
       *   <li>c<sub>1</sub>x<sub>1</sub> + ... c<sub>n</sub>x<sub>n</sub> = v</li>
       *   <li>c<sub>1</sub>x<sub>1</sub> + ... c<sub>n</sub>x<sub>n</sub> &lt;= v</li>
       *   <li>c<sub>1</sub>x<sub>1</sub> + ... c<sub>n</sub>x<sub>n</sub> &gt;= v</li>
       * </ul>
       *
       * @param coefficients The coefficients of the constraint (left hand side)
       * @param relationship The type of (in)equality used in the constraint
       * @param value The value of the constraint (right hand side)
       */
      public LinearConstraint(final RealVector coefficients,
                              final Relationship relationship,
                              final double value) {
          this.coefficients = coefficients;
          this.relationship = relationship;
          this.value        = value;
      }
  
      /**
       * Build a constraint involving two linear equations.
       * <p>
       * A linear constraint with two linear equation has one of the forms:
       * <ul>
       *   <li>l<sub>1</sub>x<sub>1</sub> + ... l<sub>n</sub>x<sub>n</sub> + l<sub>cst</sub> =
       *       r<sub>1</sub>x<sub>1</sub> + ... r<sub>n</sub>x<sub>n</sub> + r<sub>cst</sub></li>
       *   <li>l<sub>1</sub>x<sub>1</sub> + ... l<sub>n</sub>x<sub>n</sub> + l<sub>cst</sub> &lt;=
      *       r<sub>1</sub>x<sub>1</sub> + ... r<sub>n</sub>x<sub>n</sub> + r<sub>cst</sub></li>
      *   <li>l<sub>1</sub>x<sub>1</sub> + ... l<sub>n</sub>x<sub>n</sub> + l<sub>cst</sub> &gt;=
      *       r<sub>1</sub>x<sub>1</sub> + ... r<sub>n</sub>x<sub>n</sub> + r<sub>cst</sub></li>
      * </ul>
      *
      * @param lhsCoefficients The coefficients of the linear expression on the left hand side of the constraint
      * @param lhsConstant The constant term of the linear expression on the left hand side of the constraint
      * @param relationship The type of (in)equality used in the constraint
      * @param rhsCoefficients The coefficients of the linear expression on the right hand side of the constraint
      * @param rhsConstant The constant term of the linear expression on the right hand side of the constraint
      */
     public LinearConstraint(final double[] lhsCoefficients, final double lhsConstant,
                             final Relationship relationship,
                             final double[] rhsCoefficients, final double rhsConstant) {
         double[] sub = new double[lhsCoefficients.length];
         for (int i = 0; i < sub.length; ++i) {
             sub[i] = lhsCoefficients[i] - rhsCoefficients[i];
         }
         this.coefficients = new ArrayRealVector(sub, false);
         this.relationship = relationship;
         this.value        = rhsConstant - lhsConstant;
     }
 
     /**
      * Build a constraint involving two linear equations.
      * <p>
      * A linear constraint with two linear equation has one of the forms:
      * <ul>
      *   <li>l<sub>1</sub>x<sub>1</sub> + ... l<sub>n</sub>x<sub>n</sub> + l<sub>cst</sub> =
      *       r<sub>1</sub>x<sub>1</sub> + ... r<sub>n</sub>x<sub>n</sub> + r<sub>cst</sub></li>
      *   <li>l<sub>1</sub>x<sub>1</sub> + ... l<sub>n</sub>x<sub>n</sub> + l<sub>cst</sub> &lt;=
      *       r<sub>1</sub>x<sub>1</sub> + ... r<sub>n</sub>x<sub>n</sub> + r<sub>cst</sub></li>
      *   <li>l<sub>1</sub>x<sub>1</sub> + ... l<sub>n</sub>x<sub>n</sub> + l<sub>cst</sub> &gt;=
      *       r<sub>1</sub>x<sub>1</sub> + ... r<sub>n</sub>x<sub>n</sub> + r<sub>cst</sub></li>
      * </ul>
      *
      * @param lhsCoefficients The coefficients of the linear expression on the left hand side of the constraint
      * @param lhsConstant The constant term of the linear expression on the left hand side of the constraint
      * @param relationship The type of (in)equality used in the constraint
      * @param rhsCoefficients The coefficients of the linear expression on the right hand side of the constraint
      * @param rhsConstant The constant term of the linear expression on the right hand side of the constraint
      */
     public LinearConstraint(final RealVector lhsCoefficients, final double lhsConstant,
                             final Relationship relationship,
                             final RealVector rhsCoefficients, final double rhsConstant) {
         this.coefficients = lhsCoefficients.subtract(rhsCoefficients);
         this.relationship = relationship;
         this.value        = rhsConstant - lhsConstant;
     }
 
     /**
      * Gets the coefficients of the constraint (left hand side).
      *
      * @return the coefficients of the constraint (left hand side).
      */
     public RealVector getCoefficients() {
         return coefficients;
     }
 
     /**
      * Gets the relationship between left and right hand sides.
      *
      * @return the relationship between left and right hand sides.
      */
     public Relationship getRelationship() {
         return relationship;
     }
 
     /**
      * Gets the value of the constraint (right hand side).
      *
      * @return the value of the constraint (right hand side).
      */
     public double getValue() {
         return value;
     }
 
     /** {@inheritDoc} */
     @Override
     public boolean equals(Object other) {
         if (this == other) {
             return true;
         }
         if (other instanceof LinearConstraint) {
             LinearConstraint rhs = (LinearConstraint) other;
             return relationship == rhs.relationship &&
                 value == rhs.value &&
                 coefficients.equals(rhs.coefficients);
         }
         return false;
     }
 
     /** {@inheritDoc} */
     @Override
     public int hashCode() {
         return relationship.hashCode() ^
             Double.valueOf(value).hashCode() ^
             coefficients.hashCode();
     }
 }