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/* -------------------------------------------------------------------------- *
* Simbody(tm): SimTKmath *
* -------------------------------------------------------------------------- *
* This is part of the SimTK biosimulation toolkit originating from *
* Simbios, the NIH National Center for Physics-Based Simulation of *
* Biological Structures at Stanford, funded under the NIH Roadmap for *
* Medical Research, grant U54 GM072970. See https://simtk.org/home/simbody. *
* *
* Portions copyright (c) 2013 Stanford University and the Authors. *
* Authors: Michael Sherman *
* Contributors: *
* *
* Licensed under the Apache License, Version 2.0 (the "License"); you may *
* not use this file except in compliance with the License. You may obtain a *
* copy of the License at http://www.apache.org/licenses/LICENSE-2.0. *
* *
* Unless required by applicable law or agreed to in writing, software *
* distributed under the License is distributed on an "AS IS" BASIS, *
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. *
* See the License for the specific language governing permissions and *
* limitations under the License. *
* -------------------------------------------------------------------------- */
#include "simmath/SemiExplicitEulerIntegrator.h"
#include "IntegratorRep.h"
#include "SemiExplicitEulerIntegratorRep.h"
using namespace SimTK;
//==============================================================================
// SEMI EXPLICIT EULER INTEGRATOR
//==============================================================================
SemiExplicitEulerIntegrator::SemiExplicitEulerIntegrator
(const System& sys, Real stepSize) {
rep = new SemiExplicitEulerIntegratorRep(this, sys);
setFixedStepSize(stepSize);
}
//==============================================================================
// SEMI EXPLICIT EULER INTEGRATOR REP
//==============================================================================
SemiExplicitEulerIntegratorRep::SemiExplicitEulerIntegratorRep
(Integrator* handle, const System& sys)
: AbstractIntegratorRep(handle, sys, 1, 1, "SemiExplicitEuler", false)
{
}
//==============================================================================
// CREATE INTERPOLATED STATE
//==============================================================================
// Create an interpolated state at time t, which is between tPrev and tCurrent.
// If we haven't yet delivered an interpolated state in this interval, we have
// to initialize its discrete part from the advanced state.
void SemiExplicitEulerIntegratorRep::createInterpolatedState(Real t) {
const System& system = getSystem();
const State& advanced = getAdvancedState();
State& interp = updInterpolatedState();
interp = advanced; // pick up discrete stuff.
const Real weight1 = (getAdvancedTime()-t) /
(getAdvancedTime()-getPreviousTime());
const Real weight2 = 1-weight1;
interp.updY() = weight1*getPreviousY()+weight2*getAdvancedState().getY();
interp.updTime() = t;
if (userProjectInterpolatedStates == 0) {
system.realize(interp, Stage::Time);
system.prescribeQ(interp);
system.realize(interp, Stage::Position);
system.prescribeU(interp);
system.realize(interp, Stage::Velocity);
return;
}
// We may need to project onto constraint manifold. Allow project()
// to throw an exception if it fails since there is no way to recover here.
realizeAndProjectKinematicsWithThrow(interp, ProjectOptions::LocalOnly);
}
//==============================================================================
// BACK UP ADVANCED STATE BY INTERPOLATION
//==============================================================================
// Interpolate the advanced state back to an earlier part of the interval,
// forgetting about the rest of the interval. This is necessary, for
// example after we have localized an event trigger to an interval tLow:tHigh
// where tHigh < tAdvanced.
void SemiExplicitEulerIntegratorRep::
backUpAdvancedStateByInterpolation(Real t) {
const System& system = getSystem();
State& advanced = updAdvancedState();
const Real t0 = getPreviousTime(), t1 = advanced.getTime();
const Vector& y0 = getPreviousY();
const Vector& y1 = advanced.getY();
assert(t0 <= t && t <= t1);
assert(t1 > t0);
const Real weight0 = (t1-t) / (t1-t0);
const Real weight1 = 1-weight0;
advanced.updY() = weight0*y0 + weight1*y1;
advanced.updTime() = t;
// Ignore any user request not to project interpolated states here -- this
// is the actual advanced state which will be propagated through the
// rest of the trajectory so we can't allow it not to satisfy the
// constraints!
// But it is OK if it just *barely* satisfies the constraints so we
// won't get carried away if the user isn't being finicky about it.
// Project position constraints if warranted. Allow project()
// to throw an exception if it fails since there is no way to recover here.
realizeAndProjectKinematicsWithThrow(advanced, ProjectOptions::LocalOnly);
}
//==============================================================================
// ATTEMPT DAE STEP
//==============================================================================
// Note that SemiExplicitEuler overrides the entire DAE step because it can't
// use the default ODE-then-DAE structure. Instead the constraint projections
// are interwoven here.
bool SemiExplicitEulerIntegratorRep::attemptDAEStep
(Real t1, Vector& yErrEst, int& errOrder, int& numIterations)
{
const System& system = getSystem();
State& advanced = updAdvancedState();
Vector dummyErrEst; // for when we don't want the error estimate projected
statsStepsAttempted++;
const Real t0 = getPreviousTime(); // nicer names
const Vector& q0 = getPreviousQ();
const Vector& u0 = getPreviousU();
const Vector& z0 = getPreviousZ();
const Vector& qdot0 = getPreviousQDot();
const Vector& udot0 = getPreviousUDot();
const Vector& zdot0 = getPreviousZDot();
const Vector& qdotdot0 = getPreviousQDotDot();
const Real h = t1-t0;
// Advance the first order variables.
// TODO: this part should be implicit in u and z to make this symplectic
// Euler.
advanced.updZ() = getPreviousZ() + h * getPreviousZDot();
advanced.updU() = getPreviousU() + h * getPreviousUDot();
//TODO: need to be able to do this without invalidating q's.
// Should be able to calculate u_prescribed(newTime, oldQ)
advanced.updTime() = t1;
system.realize(advanced, Stage::Position); // old q, new t
system.prescribeU(advanced);
// Update qdot_t1 = N(q_t0)*u_t1 from now-advanced u.
const int nq = advanced.getNQ();
Vector qdot_t1(nq);
system.multiplyByN(advanced, advanced.getU(), qdot_t1);
advanced.updQ() = getPreviousQ() + h * qdot_t1;
system.prescribeQ(advanced);
system.realize(advanced, Stage::Position); // new q, new t
system.prescribeU(advanced); // update prescribed u in case q-dependent
// Consider position constraint projection. Note that we have to do this
// projection prior to calculating prescribed u's since the prescription
// can depend on q's. Prevent project() from throwing an exception since
// failure here may be recoverable.
bool anyChanges;
if (!localProjectQAndQErrEstNoThrow(advanced, dummyErrEst, anyChanges))
return false; // convergence failure for this step
// q's satisfy the position constraint manifold. Now work on u's.
system.prescribeU(advanced);
system.realize(advanced, Stage::Velocity);
// Now try velocity constraint projection. Nothing will happen if
// velocity constraints are already satisfied unless user has set the
// ForceProjection option.
if (!localProjectUAndUErrEstNoThrow(advanced, dummyErrEst, anyChanges))
return false; // convergence failure for this step
numIterations = 1;
return true;
}
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