MnParabolaFactory.java

package org.freehep.math.minuit;

/**
 *
 * @version $Id: MnParabolaFactory.java 8584 2006-08-10 23:06:37Z duns $
 */
abstract class MnParabolaFactory
{
   static MnParabola create(MnParabolaPoint p1, MnParabolaPoint p2, MnParabolaPoint p3)
   {
      double x1 = p1.x();
      double x2 = p2.x();
      double x3 = p3.x();
      double dx12 = x1-x2;
      double dx13 = x1-x3;
      double dx23 = x2-x3;
      
      double xm = (x1+x2+x3)/3.;
      x1 -= xm;
      x2 -= xm;
      x3 -= xm;
      
      double y1 = p1.y();
      double y2 = p2.y();
      double y3 = p3.y();
      
      double a = y1/(dx12*dx13) - y2/(dx12*dx23) + y3/(dx13*dx23);
      double b = -y1*(x2+x3)/(dx12*dx13) + y2*(x1+x3)/(dx12*dx23) - y3*(x1+x2)/(dx13*dx23);
      double c = y1 - a*x1*x1 - b*x1;
      
      c += xm*(xm*a - b);
      b -= 2.*xm*a;
      
      return new MnParabola(a, b, c);
   }
   
   static MnParabola create(MnParabolaPoint p1, double dxdy1, MnParabolaPoint p2)
   {
      double x1 = p1.x();
      double xx1 = x1*x1;
      double x2 = p2.x();
      double xx2 = x2*x2;
      double y1 = p1.y();
      double y12 = p1.y() - p2.y();
      
      double det = xx1-xx2 - 2.*x1*(x1-x2);
      double a = -(        y12 +   (x2-x1)*dxdy1)/det;
      double b = -( -2.*x1*y12 + (xx1-xx2)*dxdy1)/det;
      double c = y1 - a*xx1 - b*x1;
      
      return new MnParabola(a, b, c);
   }
}