A few fixes.

plugins/amoeba/openmmapi/include/openmm/AmoebaStretchBendForce.h

@@ -94,6 +94,24 @@ public:
     void getStretchBendParameters(int index, int& particle1, int& particle2, int& particle3, double& lengthAB,
                                   double& lengthCB, double& angle, double& k1, double& k2) const;
 
+    /**
+     * Get the force field parameters for a stretch-bend term, provided for
+     * backwards-compatibility. Since the two force constants may be different,
+     * you are recommended to call the other version of getStretchBendParameters
+     * with both a k1 and k2
+     * 
+     * @param index         the index of the stretch-bend for which to get parameters
+     * @param particle1     the index of the first particle connected by the stretch-bend
+     * @param particle2     the index of the second particle connected by the stretch-bend
+     * @param particle3     the index of the third particle connected by the stretch-bend
+     * @param lengthAB      the equilibrium length of the stretch-bend in bond ab [particle1, particle2], measured in nm
+     * @param lengthCB      the equilibrium length of the stretch-bend in bond cb [particle3, particle2], measured in nm
+     * @param angle         the equilibrium angle in radians
+     * @param k1            the force constant
+     */
+    void getStretchBendParameters(int index, int& particle1, int& particle2, int& particle3, double& lengthAB,
+                                  double& lengthCB, double& angle, double& k1) const;
+
     /**
      * Set the force field parameters for a stretch-bend term.
      * 

plugins/amoeba/platforms/cuda/src/AmoebaCudaKernels.cpp

@@ -483,7 +483,7 @@ private:
 };
 
 CudaCalcAmoebaStretchBendForceKernel::CudaCalcAmoebaStretchBendForceKernel(std::string name, const Platform& platform, CudaContext& cu, const System& system) :
-                   CalcAmoebaStretchBendForceKernel(name, platform), cu(cu), system(system), params(NULL) {
+                   CalcAmoebaStretchBendForceKernel(name, platform), cu(cu), system(system), params1(NULL), params2(NULL) {
 }
 
 CudaCalcAmoebaStretchBendForceKernel::~CudaCalcAmoebaStretchBendForceKernel() {
@@ -539,14 +539,17 @@ void CudaCalcAmoebaStretchBendForceKernel::copyParametersToContext(ContextImpl&
     
     // Record the per-stretch-bend parameters.
     
-    vector<float4> paramVector(numStretchBends);
+    vector<float3> paramVector(numStretchBends);
+    vector<float2> paramVector1(numStretchBends);
     for (int i = 0; i < numStretchBends; i++) {
         int atom1, atom2, atom3;
-        double lengthAB, lengthCB, angle, k;
-        force.getStretchBendParameters(startIndex+i, atom1, atom2, atom3, lengthAB, lengthCB, angle, k);
-        paramVector[i] = make_float4((float) lengthAB, (float) lengthCB, (float) angle, (float) k);
+        double lengthAB, lengthCB, angle, k1, k2;
+        force.getStretchBendParameters(startIndex+i, atom1, atom2, atom3, lengthAB, lengthCB, angle, k1, k2);
+        paramVector[i] = make_float3((float) lengthAB, (float) lengthCB, (float) angle);
+        paramVector1[i] = make_flaot2((float) k1, (float) k2);
     }
-    params->upload(paramVector);
+    params1->upload(paramVector);
+    params2->upload(paramVector1);
     
     // Mark that the current reordering may be invalid.
     

plugins/amoeba/platforms/reference/src/SimTKReference/AmoebaReferenceStretchBendForce.cpp

@@ -52,7 +52,7 @@ using OpenMM::RealVec;
 RealOpenMM AmoebaReferenceStretchBendForce::calculateStretchBendIxn( const RealVec& positionAtomA, const RealVec& positionAtomB,
                                                                      const RealVec& positionAtomC,
                                                                      RealOpenMM lengthAB,      RealOpenMM lengthCB,
-                                                                     RealOpenMM idealAngle,    RealOpenMM kParameter,
+                                                                     RealOpenMM idealAngle,    RealOpenMM k1Parameter,
                                                                      RealOpenMM k2Parameter, RealVec* forces ) const {
 
    // ---------------------------------------------------------------------------------------
@@ -156,7 +156,8 @@ RealOpenMM AmoebaReferenceStretchBendForce::calculateForceAndEnergy( int numStre
                                                                        const std::vector<RealOpenMM>& lengthABParameters,
                                                                        const std::vector<RealOpenMM>& lengthCBParameters,
                                                                        const std::vector<RealOpenMM>&  angle,
-                                                                       const std::vector<RealOpenMM>&  kQuadratic,
+                                                                       const std::vector<RealOpenMM>&  k1Quadratic,
+                                                                       const std::vector<RealOpenMM>&  k2Quadratic,
                                                                        vector<RealVec>& forceData) const {
     RealOpenMM energy      = 0.0; 
     for (unsigned int ii = 0; ii < static_cast<unsigned int>(numStretchBends); ii++) {
@@ -166,10 +167,11 @@ RealOpenMM AmoebaReferenceStretchBendForce::calculateForceAndEnergy( int numStre
         RealOpenMM abLength     = lengthABParameters[ii];
         RealOpenMM cbLength     = lengthCBParameters[ii];
         RealOpenMM idealAngle   = angle[ii];
-        RealOpenMM angleK       = kQuadratic[ii];
+        RealOpenMM angleK1      = k1Quadratic[ii];
+        RealOpenMM angleK2      = k2Quadratic[ii];
         RealVec forces[3];
         energy                 += calculateStretchBendIxn( posData[particle1Index], posData[particle2Index], posData[particle3Index],
-                                                           abLength, cbLength, idealAngle, angleK, forces );
+                                                           abLength, cbLength, idealAngle, angleK1, anglek2, forces );
         // accumulate forces
     
         for( int jj = 0; jj < 3; jj++ ){

plugins/amoeba/platforms/reference/src/SimTKReference/AmoebaReferenceStretchBendForce.h

@@ -77,7 +77,8 @@ public:
                                         const std::vector<RealOpenMM>& lengthABParameters,
                                         const std::vector<RealOpenMM>& lengthCBParameters,
                                         const std::vector<RealOpenMM>&  angle,
-                                        const std::vector<RealOpenMM>&  kQuadratic,
+                                        const std::vector<RealOpenMM>&  k1Quadratic,
+                                        const std::vector<RealOpenMM>&  k2Quadratic,
                                         std::vector<OpenMM::RealVec>& forceData ) const;