/**
  * Copyright (c): Uwe Schmidt, FH Wedel
  *
  * You may study, modify and distribute this source code
  * FOR NON-COMMERCIAL PURPOSES ONLY.
  * This copyright message has to remain unchanged.
  *
  * Note that this document is provided 'as is',
  * WITHOUT WARRANTY of any kind either expressed or implied.
  */

/**
  * search a zero of a function f in an intervall x1..x2
  * with intervall nesting
  */

public
class IntervallNesting
  extends SearchZero
{

  //--------------------
  //
  // Constructors

  public
  IntervallNesting() {
    super();
  }

  public
  IntervallNesting(double precision) {
    super(precision);
  }

  //--------------------

  public
  double searchZero(double x1,
		    double x2,
		    RealFunction f)
    throws NoZeroFoundException {
      double y1 = f.at(x1);
      noOfCalls = 1;

      if ( Math.abs(y1) < precision )
	  return
	      x1;

      double y2 = f.at(x2);
      noOfCalls = 2;

      if ( Math.abs(y2) < precision )
	  return
	      x2;

      if ( (y1 >= 0) == (y2 >= 0) )
	throw
	  new NoZeroFoundException(
		"function values with equal signs: "
                + "f.at(" + x1 + ") = " + y1 + ", "
                + "f.at(" + x2 + ") = " + y2 );

      while ( true ) {
	double x12 = (x2 + x1) / 2.0;
	double y12 = f.at(x12);
	++noOfCalls;

	if ( Math.abs(y12) < precision ) {
	  return
	      x12;
	}

	if ( (y1 >= 0) == (y12 >= 0) ) {
	  x1 = x12;
	  y1 = y12;
	} else {
	  x2 = x12;
	  y2 = y12;
	}

      }
  }

  //--------------------

  public
  String toString() {
    return
      "IntervallNesting with precision " + precision;
  }
}