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/*
 * Copyright (c) 2016 Jacob Rachiele
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy of this software
 * and associated documentation files (the "Software"), to deal in the Software without restriction
 * including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense
 * and/or sell copies of the Software, and to permit persons to whom the Software is furnished to
 * do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all copies or
 * substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED
 * INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
 * PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
 * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
 * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
 * USE OR OTHER DEALINGS IN THE SOFTWARE.
 *
 * Contributors:
 *
 * Jacob Rachiele
 */
package math.function;

import linear.doubles.Vector;
import optim.NumericalDerivatives;

/**
 * A partial implementation of a scalar-valued function of several variables.
 *
 */
public abstract class AbstractMultivariateFunction implements MultivariateFunction {

  private static final double gradientTolerance = 1E-3;
  
  protected int functionEvaluations = 0;
  protected int gradientEvalutations = 0;
  
  public Vector gradientAt(Vector point) {
    gradientEvalutations++;
    return NumericalDerivatives.centralDifferenceGradient(this, point, gradientTolerance);
  }
  
  public Vector gradientAt(final Vector point, final double functionValue) {
    gradientEvalutations++;
    return NumericalDerivatives.forwardDifferenceGradient(this, point, gradientTolerance * gradientTolerance,
        functionValue);
  }
  
  /**
   * The number of times this function has been evaluated.
   *
   * @return the number of times this function has been evaluated.
   */
  public int functionEvaluations() {
    return this.functionEvaluations;
  }
  
  /**
   * The number of times the gradient has been computed.
   *
   * @return the number of times the gradient has been computed.
   */
  public int gradientEvaluations() {
    return this.gradientEvalutations;
  }

}