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diff --git a/thirdparty/bullet/BulletSoftBody/btKrylovSolver.h b/thirdparty/bullet/BulletSoftBody/btKrylovSolver.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_KRYLOV_SOLVER_H
+#define BT_KRYLOV_SOLVER_H
+#include <iostream>
+#include <cmath>
+#include <limits>
+#include <LinearMath/btAlignedObjectArray.h>
+#include <LinearMath/btVector3.h>
+#include <LinearMath/btScalar.h>
+#include "LinearMath/btQuickprof.h"
+
+template <class MatrixX>
+class btKrylovSolver
+{
+	typedef btAlignedObjectArray<btVector3> TVStack;
+
+public:
+	int m_maxIterations;
+	btScalar m_tolerance;
+	btKrylovSolver(int maxIterations, btScalar tolerance)
+		: m_maxIterations(maxIterations), m_tolerance(tolerance)
+	{
+	}
+
+	virtual ~btKrylovSolver() {}
+
+	virtual int solve(MatrixX& A, TVStack& x, const TVStack& b, bool verbose = false) = 0;
+
+	virtual void reinitialize(const TVStack& b) = 0;
+
+	virtual SIMD_FORCE_INLINE TVStack sub(const TVStack& a, const TVStack& b)
+	{
+		// c = a-b
+		btAssert(a.size() == b.size());
+		TVStack c;
+		c.resize(a.size());
+		for (int i = 0; i < a.size(); ++i)
+		{
+			c[i] = a[i] - b[i];
+		}
+		return c;
+	}
+
+	virtual SIMD_FORCE_INLINE btScalar squaredNorm(const TVStack& a)
+	{
+		return dot(a, a);
+	}
+
+	virtual SIMD_FORCE_INLINE btScalar norm(const TVStack& a)
+	{
+		btScalar ret = 0;
+		for (int i = 0; i < a.size(); ++i)
+		{
+			for (int d = 0; d < 3; ++d)
+			{
+				ret = btMax(ret, btFabs(a[i][d]));
+			}
+		}
+		return ret;
+	}
+
+	virtual SIMD_FORCE_INLINE btScalar dot(const TVStack& a, const TVStack& b)
+	{
+		btScalar ans(0);
+		for (int i = 0; i < a.size(); ++i)
+			ans += a[i].dot(b[i]);
+		return ans;
+	}
+
+	virtual SIMD_FORCE_INLINE void multAndAddTo(btScalar s, const TVStack& a, TVStack& result)
+	{
+		//        result += s*a
+		btAssert(a.size() == result.size());
+		for (int i = 0; i < a.size(); ++i)
+			result[i] += s * a[i];
+	}
+
+	virtual SIMD_FORCE_INLINE TVStack multAndAdd(btScalar s, const TVStack& a, const TVStack& b)
+	{
+		// result = a*s + b
+		TVStack result;
+		result.resize(a.size());
+		for (int i = 0; i < a.size(); ++i)
+			result[i] = s * a[i] + b[i];
+		return result;
+	}
+
+	virtual SIMD_FORCE_INLINE void setTolerance(btScalar tolerance)
+	{
+		m_tolerance = tolerance;
+	}
+};
+#endif /* BT_KRYLOV_SOLVER_H */