lcsim/src/org/lcsim/util/swim

diff -u -r1.14 -r1.15
--- Helix.java	19 Oct 2005 10:32:53 -0000	1.14
+++ Helix.java	26 Oct 2005 00:36:23 -0000	1.15
@@ -20,7 +20,7 @@

  * All quantities in this class are dimensionless. It has no dependencies
  * except for Hep3Vector (which could easily be removed).
  * @author tonyj

- * @version $Id: Helix.java,v 1.14 2005/10/19 10:32:53 jstrube Exp $

+ * @version $Id: Helix.java,v 1.15 2005/10/26 00:36:23 jstrube Exp $

  */
 public class Helix implements Trajectory
 {

@@ -99,9 +99,10 @@

     */
    public double getDistanceToPoint(Hep3Vector point) {
        double tanLambda = sinLambda/cosLambda;

-       double px = abs(radius)*cosPhi;
-       double py = abs(radius)*sinPhi;
-       double pz = abs(radius)*tanLambda;

+       double r = abs(radius);
+       double px = r*cosPhi;
+       double py = r*sinPhi;
+       double pz = r*tanLambda;

        double rho = -cosLambda/radius;       
        double pMag = sqrt(px*px + py*py + pz*pz);
        Hep3Vector p0 = new BasicHep3Vector(px, py, pz);       

@@ -142,9 +143,10 @@

     */
    public double getSignedClosestDifferenceToPoint(Hep3Vector point) {
        double tanLambda = sinLambda/cosLambda;

-       double px = abs(radius)*cosPhi;
-       double py = abs(radius)*sinPhi;
-       double pz = abs(radius)*tanLambda;

+       double r = abs(radius);
+       double px = r*cosPhi;
+       double py = r*sinPhi;
+       double pz = r*tanLambda;

        double rho = -cosLambda/radius;
        Hep3Vector pCrossB = new BasicHep3Vector(py, -px, 0);
        Hep3Vector xDiff = VecOp.sub(origin, point);

@@ -170,10 +172,11 @@

 
    // Returns the "momentum" at the length s from the starting point.
    // This uses the definition in http://www.phys.ufl.edu/~avery/fitting/transport.pdf

-   Hep3Vector getMomentumAtDistance(double s) {
-	   double p0x = radius*cosPhi;
-	   double p0y = radius*sinPhi;
-	   double p0z = radius*sinLambda/cosLambda;

+   public Hep3Vector getTangentAtDistance(double s) {
+       double r = abs(radius);
+	   double p0x = r*cosPhi;
+	   double p0y = r*sinPhi;
+	   double p0z = r*sinLambda/cosLambda;

 	   double rho = -cosLambda/radius;
 	   
 	   double px = p0x*cos(rho*s) - p0y*sin(rho*s);

lcsim/test/org/lcsim/util/swim

diff -u -r1.8 -r1.9
--- HelixTest.java	19 Oct 2005 10:34:38 -0000	1.8
+++ HelixTest.java	26 Oct 2005 00:36:24 -0000	1.9
@@ -12,7 +12,7 @@

 /**
  *
  * @author tonyj

- * @version $Id: HelixTest.java,v 1.8 2005/10/19 10:34:38 jstrube Exp $

+ * @version $Id: HelixTest.java,v 1.9 2005/10/26 00:36:24 jstrube Exp $

  */
 public class HelixTest extends TestCase
 {

@@ -275,6 +275,25 @@

        }
    }
 

+   public void testGetTangentAtDistance() {
+       Hep3Vector origin = new BasicHep3Vector(3, 6, 9);
+       double radius = -1.7;
+       double phi = Math.PI/4;
+       double lambda = Math.PI/4;
+       Helix helix1 = new Helix(origin, radius, phi, lambda);
+       Helix helix2 = new Helix(origin, -radius, phi, lambda);
+       
+       // momentum conservation
+       for (int i=0; i<25; ++i) {
+           Hep3Vector tangentAtThisPiece_1 = helix1.getTangentAtDistance(i*.37); 
+           Hep3Vector tangentAtThisPiece_2 = helix2.getTangentAtDistance(i*.37); 
+           assertEquals(tangentAtThisPiece_1.magnitude(), helix1.getTangentAtDistance((i+1)*.37).magnitude());
+           assertEquals(tangentAtThisPiece_2.magnitude(), helix2.getTangentAtDistance(i*.37).magnitude());
+           assertEquals(tangentAtThisPiece_1.z(), tangentAtThisPiece_2.z());
+       }
+   }
+   
+   

    private void assertEquals(Hep3Vector v1, Hep3Vector v2)
    {
       assertEquals(v1.x(),v2.x(), 1e-14);