Inductor.java

class Inductor {
    public static final int FLAG_BACK_EULER = 2;
    int nodes[];
    int flags;
    CirSim sim;
    
    double inductance;
    double compResistance, current;
    double curSourceValue;
    Inductor(CirSim s) {
	sim = s;
	nodes = new int[2];
    }
    void setup(double ic, double cr, int f) {
	inductance = ic;
	current = cr;
	flags = f;
    }
    boolean isTrapezoidal() { return (flags & FLAG_BACK_EULER) == 0; }
    void reset() {
	current = 0;
    }
    void stamp(int n0, int n1) {
	// inductor companion model using trapezoidal or backward euler
	// approximations (Norton equivalent) consists of a current
	// source in parallel with a resistor.  Trapezoidal is more
	// accurate than backward euler but can cause oscillatory behavior.
	// The oscillation is a real problem in circuits with switches.
	nodes[0] = n0;
	nodes[1] = n1;
	if (isTrapezoidal())
	    compResistance = 2*inductance/sim.timeStep;
	else // backward euler
	    compResistance = inductance/sim.timeStep;
	sim.stampResistor(nodes[0], nodes[1], compResistance);
	sim.stampRightSide(nodes[0]);
	sim.stampRightSide(nodes[1]);
    }
    boolean nonLinear() { return false; }

    void startIteration(double voltdiff) {
	if (isTrapezoidal())
	    curSourceValue = voltdiff/compResistance+current;
	else // backward euler
	    curSourceValue = current;
    }
    
    double calculateCurrent(double voltdiff) {
	// we check compResistance because this might get called
	// before stamp(), which sets compResistance, causing
	// infinite current
	if (compResistance > 0)
	    current = voltdiff/compResistance + curSourceValue;
	return current;
    }
    void doStep(double voltdiff) {
	sim.stampCurrentSource(nodes[0], nodes[1], curSourceValue);
    }
}