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      1 /*
      2 Bullet Continuous Collision Detection and Physics Library
      3 Copyright (c) 2003-2013 Erwin Coumans  http://bulletphysics.org
      4 
      5 This software is provided 'as-is', without any express or implied warranty.
      6 In no event will the authors be held liable for any damages arising from the use of this software.
      7 Permission is granted to anyone to use this software for any purpose,
      8 including commercial applications, and to alter it and redistribute it freely,
      9 subject to the following restrictions:
     10 
     11 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.
     12 2. Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software.
     13 3. This notice may not be removed or altered from any source distribution.
     14 */
     15 ///original version written by Erwin Coumans, October 2013
     16 
     17 #ifndef BT_SOLVE_PROJECTED_GAUSS_SEIDEL_H
     18 #define BT_SOLVE_PROJECTED_GAUSS_SEIDEL_H
     19 
     20 
     21 #include "btMLCPSolverInterface.h"
     22 
     23 ///This solver is mainly for debug/learning purposes: it is functionally equivalent to the btSequentialImpulseConstraintSolver solver, but much slower (it builds the full LCP matrix)
     24 class btSolveProjectedGaussSeidel : public btMLCPSolverInterface
     25 {
     26 public:
     27 	virtual bool solveMLCP(const btMatrixXu & A, const btVectorXu & b, btVectorXu& x, const btVectorXu & lo,const btVectorXu & hi,const btAlignedObjectArray<int>& limitDependency, int numIterations, bool useSparsity = true)
     28 	{
     29 		if (!A.rows())
     30 			return true;
     31 		//the A matrix is sparse, so compute the non-zero elements
     32 		A.rowComputeNonZeroElements();
     33 
     34 		//A is a m-n matrix, m rows, n columns
     35 		btAssert(A.rows() == b.rows());
     36 
     37 		int i, j, numRows = A.rows();
     38 
     39 		float delta;
     40 
     41 		for (int k = 0; k <numIterations; k++)
     42 		{
     43 			for (i = 0; i <numRows; i++)
     44 			{
     45 				delta = 0.0f;
     46 				if (useSparsity)
     47 				{
     48 					for (int h=0;h<A.m_rowNonZeroElements1[i].size();h++)
     49 					{
     50 						int j = A.m_rowNonZeroElements1[i][h];
     51 						if (j != i)//skip main diagonal
     52 						{
     53 							delta += A(i,j) * x[j];
     54 						}
     55 					}
     56 				} else
     57 				{
     58 					for (j = 0; j <i; j++)
     59 						delta += A(i,j) * x[j];
     60 					for (j = i+1; j<numRows; j++)
     61 						delta += A(i,j) * x[j];
     62 				}
     63 
     64 				float aDiag = A(i,i);
     65 				x [i] = (b [i] - delta) / aDiag;
     66 				float s = 1.f;
     67 
     68 				if (limitDependency[i]>=0)
     69 				{
     70 					s = x[limitDependency[i]];
     71 					if (s<0)
     72 						s=1;
     73 				}
     74 
     75 				if (x[i]<lo[i]*s)
     76 					x[i]=lo[i]*s;
     77 				if (x[i]>hi[i]*s)
     78 					x[i]=hi[i]*s;
     79 			}
     80 		}
     81 		return true;
     82 	}
     83 
     84 };
     85 
     86 #endif //BT_SOLVE_PROJECTED_GAUSS_SEIDEL_H
     87