integrator-force-rk4.cpp

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/*
 * Copyright 2010,
 * François Bleibel,
 * Olivier Stasse,
 *
 * CNRS/AIST
 *
 */
 
#include <dynamic-graph/factory.h>
#include <sot/dynamic-pinocchio/integrator-force-rk4.h>
 
#include <sot/core/debug.hh>
 
using namespace dynamicgraph::sot;
using namespace dynamicgraph;
DYNAMICGRAPH_FACTORY_ENTITY_PLUGIN(IntegratorForceRK4, "IntegratorForceRK4");
 
IntegratorForceRK4::IntegratorForceRK4(const std::string& name)
    : IntegratorForce(name) {
  sotDEBUGIN(5);
 
  velocityDerivativeSOUT.setFunction(
      boost::bind(&IntegratorForceRK4::computeDerivativeRK4, this, _1, _2));
 
  sotDEBUGOUT(5);
}
 
IntegratorForceRK4::~IntegratorForceRK4(void) {
  sotDEBUGIN(5);
 
  sotDEBUGOUT(5);
  return;
}
 
/* --- SIGNALS -------------------------------------------------------------- */
/* --- SIGNALS -------------------------------------------------------------- */
/* --- SIGNALS -------------------------------------------------------------- */
 
/* The derivative of the signal is such that: M v_dot + B v = f. We deduce:
 * v_dot =  M^-1 (f - Bv)
 * Using RK4 method (doc: wikipedia ;) ): dv= dt/6 ( k1 + 2.k2 + 2.k3 + k4)
 */
static const double rk_fact[4] = {1., 2., 2., 1.};
 
dynamicgraph::Vector& IntegratorForceRK4::computeDerivativeRK4(
    dynamicgraph::Vector& res, const sigtime_t& time) {
  sotDEBUGIN(15);
 
  const dynamicgraph::Vector& force = forceSIN(time);
  const dynamicgraph::Matrix& massInverse = massInverseSIN(time);
  const dynamicgraph::Matrix& friction = frictionSIN(time);
  long int nf = force.size(), nv = friction.cols();
  res.resize(nv);
  res.fill(0);
 
  if (!velocityPrecSIN) {
    dynamicgraph::Vector zero(nv);
    zero.fill(0);
    velocityPrecSIN = zero;
  }
  const dynamicgraph::Vector& vel = velocityPrecSIN(time);
  double& dt = this->IntegratorForce::timeStep;  // this is &
 
  sotDEBUG(15) << "force = " << force;
  sotDEBUG(15) << "vel = " << vel;
  sotDEBUG(25) << "Mi = " << massInverse;
  sotDEBUG(25) << "B = " << friction;
  sotDEBUG(25) << "dt = " << dt << std::endl;
 
  std::vector<dynamicgraph::Vector> v(4);
  dynamicgraph::Vector ki(nv), fi(nf);
  double sumFact = 0;
  v[0] = vel;
 
  for (unsigned int i = 0; i < 4; ++i) {
    sotDEBUG(35) << "v" << i << " = " << v[i];
    fi = friction * v[i];
    fi *= -1;
    fi += force;
    sotDEBUG(35) << "f" << i << " = " << fi;
    ki = massInverse * fi;
    sotDEBUG(35) << "k" << i << " = " << ki;
    if (i + 1 < 4) {
      v[i + 1] = ki;
      v[i + 1] *= (dt / rk_fact[i + 1]);
      v[i + 1] += vel;
    }
    ki *= rk_fact[i];
    res += ki;
    sotDEBUG(35) << "sum_k" << i << " = " << res;
    sumFact += rk_fact[i];
  }
 
  sotDEBUG(35) << "sum_ki = " << res;
  res *= (1 / sumFact);
 
  sotDEBUGOUT(15);
  return res;
}