/// <summary>
/// Evaluate the provided IBlackBox.
/// </summary>
public FitnessInfo Evaluate(IBlackBox box)
{
_evalCount++;
// Initialise state.
SinglePoleStateData state = new SinglePoleStateData();
state._poleAngle = SixDegrees;
// Run the pole-balancing simulation.
int timestep = 0;
for (; timestep < _maxTimesteps; timestep++)
{
// Provide state info to the black box inputs (normalised to +-1.0).
box.InputSignalArray[0] = state._cartPosX / _trackLengthHalf; // cart_pos_x range is +-trackLengthHalfed. Here we normalize it to [-1,1].
box.InputSignalArray[1] = state._cartVelocityX / 0.75; // cart_velocity_x is typically +-0.75
box.InputSignalArray[2] = state._poleAngle / TwelveDegrees; // pole_angle is +-twelve_degrees. Values outside of this range stop the simulation.
box.InputSignalArray[3] = state._poleAngularVelocity; // pole_angular_velocity is typically +-1.0 radians. No scaling required.
// Activate the network.
box.Activate();
// Calculate state at next timestep given the black box's output action (push left or push right).
SimulateTimestep(state, box.OutputSignalArray[0] > 0.5);
// Check for failure state. Has the cart run off the ends of the track or has the pole
// angle gone beyond the threshold.
if ((state._cartPosX < -_trackLengthHalf) || (state._cartPosX > _trackLengthHalf) ||
(state._poleAngle > _poleAngleThreshold) || (state._poleAngle < -_poleAngleThreshold))
{
break;
}
}
if (timestep == _maxTimesteps)
{
_stopConditionSatisfied = true;
}
// The controller's fitness is defined as the number of timesteps that elapse before failure.
double fitness = timestep;
return(new FitnessInfo(fitness, fitness));
}
/// <summary>
/// Calculates a state update for the next timestep using current model state and a single 'action' from the
/// controller. The action specifies if the controller is pushing the cart left or right. Note that this is a binary
/// action and therefore full force is always applied to the cart in some direction. This is the standard model for
/// the single pole balancing task.
/// </summary>
/// <param name="state">Model state.</param>
/// <param name="action">push direction, left(false) or right(true). Force magnitude is fixed.</param>
private void SimulateTimestep(SinglePoleStateData state, bool action)
{
//float xacc,thetaacc,force,costheta,sintheta,temp;
double force = action ? ForceMag : -ForceMag;
double cosTheta = Math.Cos(state._poleAngle);
double sinTheta = Math.Sin(state._poleAngle);
double tmp = (force + (PoleMassLength * state._poleAngularVelocity * state._poleAngularVelocity * sinTheta)) / TotalMass;
double thetaAcc = ((Gravity * sinTheta) - (cosTheta * tmp))
/ (Length * (FourThirds - ((MassPole * cosTheta * cosTheta) / TotalMass)));
double xAcc = tmp - ((PoleMassLength * thetaAcc * cosTheta) / TotalMass);
// Update the four state variables, using Euler's method.
state._cartPosX += TimeDelta * state._cartVelocityX;
state._cartVelocityX += TimeDelta * xAcc;
state._poleAngle += TimeDelta * state._poleAngularVelocity;
state._poleAngularVelocity += TimeDelta * thetaAcc;
state._action = action;
}
