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diff --git a/thirdparty/bullet/BulletSoftBody/btDeformableBackwardEulerObjective.h b/thirdparty/bullet/BulletSoftBody/btDeformableBackwardEulerObjective.h
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+/*
+ Written by Xuchen Han <xuchenhan2015@u.northwestern.edu>
+ 
+ Bullet Continuous Collision Detection and Physics Library
+ Copyright (c) 2019 Google Inc. http://bulletphysics.org
+ This software is provided 'as-is', without any express or implied warranty.
+ In no event will the authors be held liable for any damages arising from the use of this software.
+ Permission is granted to anyone to use this software for any purpose,
+ including commercial applications, and to alter it and redistribute it freely,
+ subject to the following restrictions:
+ 1. The origin of this software must not be misrepresented; you must not claim that you wrote the original software. If you use this software in a product, an acknowledgment in the product documentation would be appreciated but is not required.
+ 2. Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software.
+ 3. This notice may not be removed or altered from any source distribution.
+ */
+
+#ifndef BT_BACKWARD_EULER_OBJECTIVE_H
+#define BT_BACKWARD_EULER_OBJECTIVE_H
+#include "btConjugateGradient.h"
+#include "btDeformableLagrangianForce.h"
+#include "btDeformableMassSpringForce.h"
+#include "btDeformableGravityForce.h"
+#include "btDeformableCorotatedForce.h"
+#include "btDeformableLinearElasticityForce.h"
+#include "btDeformableNeoHookeanForce.h"
+#include "btDeformableContactProjection.h"
+#include "btPreconditioner.h"
+#include "btDeformableMultiBodyDynamicsWorld.h"
+#include "LinearMath/btQuickprof.h"
+
+class btDeformableBackwardEulerObjective
+{
+public:
+    typedef btAlignedObjectArray<btVector3> TVStack;
+    btScalar m_dt;
+    btAlignedObjectArray<btDeformableLagrangianForce*> m_lf;
+    btAlignedObjectArray<btSoftBody *>& m_softBodies;
+    Preconditioner* m_preconditioner;
+    btDeformableContactProjection m_projection;
+    const TVStack& m_backupVelocity;
+    btAlignedObjectArray<btSoftBody::Node* > m_nodes;
+    bool m_implicit;
+
+    btDeformableBackwardEulerObjective(btAlignedObjectArray<btSoftBody *>& softBodies, const TVStack& backup_v);
+    
+    virtual ~btDeformableBackwardEulerObjective();
+    
+    void initialize(){}
+    
+    // compute the rhs for CG solve, i.e, add the dt scaled implicit force to residual
+    void computeResidual(btScalar dt, TVStack& residual);
+    
+    // add explicit force to the velocity
+    void applyExplicitForce(TVStack& force);
+    
+    // apply force to velocity and optionally reset the force to zero
+    void applyForce(TVStack& force, bool setZero);
+    
+    // compute the norm of the residual
+    btScalar computeNorm(const TVStack& residual) const;
+    
+    // compute one step of the solve (there is only one solve if the system is linear)
+    void computeStep(TVStack& dv, const TVStack& residual, const btScalar& dt);
+    
+    // perform A*x = b
+    void multiply(const TVStack& x, TVStack& b) const;
+    
+    // set initial guess for CG solve
+    void initialGuess(TVStack& dv, const TVStack& residual);
+    
+    // reset data structure and reset dt
+    void reinitialize(bool nodeUpdated, btScalar dt);
+    
+    void setDt(btScalar dt);
+    
+    // add friction force to residual
+    void applyDynamicFriction(TVStack& r);
+    
+    // add dv to velocity
+    void updateVelocity(const TVStack& dv);
+    
+    //set constraints as projections
+    void setConstraints();
+    
+    // update the projections and project the residual
+    void project(TVStack& r)
+    {
+        BT_PROFILE("project");
+        m_projection.project(r);
+    }
+    
+    // perform precondition M^(-1) x = b
+    void precondition(const TVStack& x, TVStack& b)
+    {
+        m_preconditioner->operator()(x,b);
+    }
+
+    // reindex all the vertices 
+    virtual void updateId()
+    {
+        size_t node_id = 0;
+        size_t face_id = 0;
+        m_nodes.clear();
+        for (int i = 0; i < m_softBodies.size(); ++i)
+        {
+            btSoftBody* psb = m_softBodies[i];
+            for (int j = 0; j < psb->m_nodes.size(); ++j)
+            {
+                psb->m_nodes[j].index = node_id;
+                m_nodes.push_back(&psb->m_nodes[j]);
+                ++node_id;
+            }
+            for (int j = 0; j < psb->m_faces.size(); ++j)
+            {
+                psb->m_faces[j].m_index = face_id;
+                ++face_id;
+            }
+        }
+    }
+    
+    const btAlignedObjectArray<btSoftBody::Node*>* getIndices() const
+    {
+        return &m_nodes;
+    }
+    
+    void setImplicit(bool implicit)
+    {
+        m_implicit = implicit;
+    }
+
+    // Calculate the total potential energy in the system
+    btScalar totalEnergy(btScalar dt);
+};
+
+#endif /* btBackwardEulerObjective_h */