public ParametricEquation(String equ_x, String equ_y, double tstart, double tend, double dt){
		this.tstart = tstart;
		this.tend = tend;
		this.dt = dt;
		
		equx = new Equation(equ_x);
		equy = new Equation(equ_y);
		Vector<Variable> variables = equx.getVariables();
		if(variables.size()!=1)
			throw new EquationException("Invalid X Equation: " + equ_x);
		tx = variables.firstElement();
		if(!tx.getName().equals("t"))
			throw new EquationException("Invalid X Equation: " + equ_x);
		
		variables = equy.getVariables();
		if(variables.size()!=1)
			throw new EquationException("Invalid Y Equation: " + equ_y);
		ty = variables.firstElement();
		if(!ty.getName().equals("t"))
			throw new EquationException("Invalid Y Equation: " + equ_y);
	}