fixing #162; was introduced when both SBend and RBend were rewritten to be...

fixing #162; was introduced when both SBend and RBend were rewritten to be derived from 'Bend' class

src/Classic/AbsBeamline/Bend.cpp

@@ -1073,6 +1073,7 @@ bool Bend::FindIdealBendParameters(double chordLength) {
             bendAngle = 2.0 * Physics::pi - bendAngle;
 
         angle_m = bendAngle;
+
         return false;
 
     } else {
@@ -1538,6 +1539,9 @@ bool Bend::SetupBendGeometry(Inform &msg, double &startField, double &endField)
     }
 
     reinitialize_m = FindIdealBendParameters(chordLength);
+    if (getType() == RBEND) {
+        SetEntranceAngle(getEntranceAngle());
+    }
     FindReferenceExitOrigin(xExit_m, zExit_m);
 
     /*

src/Classic/AbsBeamline/Bend.h

@@ -141,6 +141,10 @@ protected:
     double getLength();
     double getMapLength();
 
+    double bX_m;                /// Amplitude of Bx field (T).
+    double bY_m;                /// Amplitude of By field (T).
+    double designEnergy_m;      /// Bend design energy (eV).
+
 private:
 
     // Not implemented.
@@ -214,11 +218,8 @@ private:
     double angle_m;             /// Bend angle for reference particle with bend
     /// design energy (radians).
     double aperture_m;          /// Aperture of magnet in non-bend plane.
-    double designEnergy_m;      /// Bend design energy (eV).
     double designRadius_m;      /// Bend design radius (m).
     double fieldAmplitude_m;    /// Amplitude of magnet field (T).
-    double bX_m;                /// Amplitude of Bx field (T).
-    double bY_m;                /// Amplitude of By field (T).
     bool angleGreaterThanPi_m;  /// Set to true if bend angle is greater than
     /// 180 degrees.
     double entranceAngle_m;     /// Angle between incoming reference trajectory

src/Classic/AbsBeamline/RBend.cpp

@@ -153,8 +153,21 @@ bool RBend::FindChordLength(Inform &msg,
      * Find bend chord length. If this was not set by the user using the
      * L (length) attribute, infer it from the field map.
      */
-    chordLength = 2 * getLength() * sin(0.5 * std::abs(getAngle())) /
-        (sin(getEntranceAngle()) + sin(std::abs(getAngle()) - getEntranceAngle()));
+    const double angle = getAngle();
+    if (std::abs(angle) > 0.0) {
+        chordLength = 2 * getLength() * sin(0.5 * std::abs(angle)) /
+            (sin(getEntranceAngle()) + sin(std::abs(angle) - getEntranceAngle()));
+    } else {
+        double refMass  = RefPartBunch_m->getM();
+        double refGamma = designEnergy_m / refMass + 1.0;
+        double refBetaGamma = sqrt(pow(refGamma, 2.0) - 1.0);
+        double refCharge = RefPartBunch_m->getQ();
+        double amplitude = (std::abs(bY_m) > 0.0? bY_m: bX_m);
+        double fieldAmplitude = refCharge * std::abs(amplitude / refCharge);
+        double designRadius = std::abs(refBetaGamma * refMass / (Physics::c * fieldAmplitude));
+        chordLength = sin(0.5 * (asin(getLength() / designRadius - sin(getEntranceAngle())) + getEntranceAngle())) * 2 * designRadius;
+    }
+
     if(chordLength > 0.0) {
         chordLengthFromMap = false;
         return true;