improvedregulafalsirootfinder.java

一个一元曲线多项式数值演示例子

package numbercruncher.mathutils;

/**
 * The root finder class that implements the
 * improved regula falsi algorithm.
 */
public class ImprovedRegulaFalsiRootFinder
    extends RegulaFalsiRootFinder {
  /** previous f(xFalse) value */
  private float prevFFalse;

  private boolean decreasePos = false;
  private boolean decreaseNeg = false;

  /**
   * Constructor.
   * @param function the functions whose roots to find
   * @param xMin the initial x-value where the function is negative
   * @param xMax the initial x-value where the function is positive
   * @throws RootFinder.InvalidIntervalException
   */
  public ImprovedRegulaFalsiRootFinder(Function function,
                                       float xMin, float xMax) throws
      RootFinder.InvalidIntervalException {
    super(function, xMin, xMax);
  }

  //----------------------------------------//
  // Override RegulaFalsiRootFinder methods //
  //----------------------------------------//

  /**
   * Do the improved regula falsi iteration procedure.
   * @param n the iteration count
   */
  protected void doIterationProcedure(int n) {
    super.doIterationProcedure(n);

    // Decrease the slope of the secant?
    if (decreasePos) {
      fPos /= 2;
    }
    if (decreaseNeg) {
      fNeg /= 2;
    }
  }

  /**
   * Compute the next position of xFalse.
   */
  protected void computeNextPosition() {
    prevXFalse = xFalse;
    prevFFalse = fFalse;
    xFalse = xPos - fPos * (xNeg - xPos) / (fNeg - fPos);
    fFalse = function.at(xFalse);

    decreasePos = decreaseNeg = false;

    // If there was no sign change in f(xFalse),
    // or if this is the first iteration step,
    // then decrease the slope of the secant.
    if (Float.isNaN(prevFFalse) || (prevFFalse * fFalse > 0)) {
      if (fFalse < 0) {
        decreasePos = true;
      }
      else {
        decreaseNeg = true;
      }
    }
  }
}