public ParametricPolarEquation(String equ_theta, String equ_r, double tstart, double tend, double dt){
		this.tstart = tstart;
		this.tend = tend;
		this.dt = dt;
		
		equtheta = new Equation(equ_theta);
		equr = new Equation(equ_r);
		Vector<Variable> variables = equtheta.getVariables();
		if(variables.size()==0){
			t_theta = new Variable("t");
		}
		else{
			if(variables.size()!=1)
				throw new EquationException("Invalid Theta Equation: " + equ_theta);
			t_theta = variables.firstElement();
			if(!t_theta.getName().equals("t"))
				throw new EquationException("Invalid Theta Equation: " + equ_theta);
		}
			variables = equr.getVariables();
		if(variables.size()==0){
			t_r = new Variable("r");
		}
		else{
			if(variables.size()!=1)
				throw new EquationException("Invalid R Equation: " + equ_r);
			t_r = variables.firstElement();
			if(!t_r.getName().equals("t"))
				throw new EquationException("Invalid R Equation: " + equ_r);
		}
	}