package joptima.functions;

import joptima.*;

/**
 * A two-dimensional sum of two one-dimensional {@link Function}s.
 * In other words, z = xfunction(x) + yfunction(y).  Either xfunction
 * or yfunction may be null.
 *
 * @author Dejan Vucinic <dvucinic@users.sourceforge.net>
 */
public class Sum2D implements Function2D {

  Function m_xfunction = null;
  Function m_yfunction = null;

  String m_name = null;

  /**
   * Constructor.
   * @param xfunction the function to extend along the y axis
   * @param yfunction the function to extend along the x axis
   */
  public Sum2D(Function xfunction, Function yfunction) {
    m_xfunction = xfunction;
    m_yfunction = yfunction;
  }

  /**
   * Calculates the value of the function at the given x-y point using the
   * preset parameters.
   * The returned value is the sum of xfunction(x) and yfunction(y).
   * @param x the x coordinate to calculate the function at
   * @param y the y coordinate to calculate the function at
   * @return the value of the function at the given x-y point
   */
  public double /* z = */ calculate(double x, double y) {
    double value = 0;
    if (null != m_xfunction) value += m_xfunction.calculate(x);
    if (null != m_yfunction) value += m_yfunction.calculate(y);
    return value;
  }

  public Parameter[] getParameters() {
    int nparams = 0;
    if (null != m_xfunction) nparams += m_xfunction.getParameters().length;
    if (null != m_yfunction) nparams += m_yfunction.getParameters().length;
    Parameter[] ret = new Parameter[nparams]; int counter = 0;
    if (null != m_xfunction) {
      for (int i = 0; i < m_xfunction.getParameters().length; i++) {
        ret[counter++] = m_xfunction.getParameters()[i];
      }
    }
    if (null != m_yfunction) {
      for (int i = 0; i < m_yfunction.getParameters().length; i++) {
        ret[counter++] = m_yfunction.getParameters()[i];
      }
    }
    return ret;
  }

  public double /* y = */ calculate(double x) {
    throw new UnsupportedOperationException("Don't know what to calculate from a single parameter.");
  }

  public String getName() {
    if (null != m_name) return m_name;

    StringBuffer ret = new StringBuffer();
    if (null != m_xfunction) {
      ret.append(m_xfunction.getName());
    }
    if (null != m_xfunction && null != m_yfunction) {
      ret.append(" + ");
    }
    if (null != m_yfunction) {
      ret.append(m_yfunction.getName());
    }
    return ret.toString();
  }

  public void setName(String newname) {
    m_name = newname;
  }

}