btDantzigLCP.h

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/*************************************************************************
 *                                                                       *
 * Open Dynamics Engine, Copyright (C) 2001,2002 Russell L. Smith.       *
 * All rights reserved.  Email: russ@q12.org   Web: www.q12.org          *
 *                                                                       *
 * This library is free software; you can redistribute it and/or         *
 * modify it under the terms of                                          * 
 *   The BSD-style license that is included with this library in         *
 *   the file LICENSE-BSD.TXT.                                           *
 *                                                                       *
 * This library is distributed in the hope that it will be useful,       *
 * but WITHOUT ANY WARRANTY; without even the implied warranty of        *
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the files    *
 * LICENSE.TXT and LICENSE-BSD.TXT for more details.                     *
 *                                                                       *
 *************************************************************************/
 
/*
 
given (A,b,lo,hi), solve the LCP problem: A*x = b+w, where each x(i),w(i)
satisfies one of
        (1) x = lo, w >= 0
        (2) x = hi, w <= 0
        (3) lo < x < hi, w = 0
A is a matrix of dimension n*n, everything else is a vector of size n*1.
lo and hi can be +/- dInfinity as needed. the first `nub' variables are
unbounded, i.e. hi and lo are assumed to be +/- dInfinity.
 
we restrict lo(i) <= 0 and hi(i) >= 0.
 
the original data (A,b) may be modified by this function.
 
if the `findex' (friction index) parameter is nonzero, it points to an array
of index values. in this case constraints that have findex[i] >= 0 are
special. all non-special constraints are solved for, then the lo and hi values
for the special constraints are set:
  hi[i] = abs( hi[i] * x[findex[i]] )
  lo[i] = -hi[i]
and the solution continues. this mechanism allows a friction approximation
to be implemented. the first `nub' variables are assumed to have findex < 0.
 
*/
 
#ifndef _BT_LCP_H_
#define _BT_LCP_H_
 
#include <stdlib.h>
#include <stdio.h>
#include <assert.h>
 
#include "LinearMath/btScalar.h"
#include "LinearMath/btAlignedObjectArray.h"
 
struct btDantzigScratchMemory
{
        btAlignedObjectArray<btScalar> m_scratch;
        btAlignedObjectArray<btScalar> L;
        btAlignedObjectArray<btScalar> d;
        btAlignedObjectArray<btScalar> delta_w;
        btAlignedObjectArray<btScalar> delta_x;
        btAlignedObjectArray<btScalar> Dell;
        btAlignedObjectArray<btScalar> ell;
        btAlignedObjectArray<btScalar *> Arows;
        btAlignedObjectArray<int> p;
        btAlignedObjectArray<int> C;
        btAlignedObjectArray<bool> state;
};
 
//return false if solving failed
bool btSolveDantzigLCP(int n, btScalar *A, btScalar *x, btScalar *b, btScalar *w,
                                           int nub, btScalar *lo, btScalar *hi, int *findex, btDantzigScratchMemory &scratch);
 
#endif  //_BT_LCP_H_