function varargout = rccirc(t,q,flag,a)
% dq = rccirc(t,q,flag,a)
% Differential equation for charge on
% capacitor in driven RC circuit

if (nargin < 4)
  a = 0.01;
end

if nargin < 3
	flag = '';
end
%
switch flag
  case ''
    varargout{1} = f(t,q,a);
  case 'jacobian'
    varargout{1} = jacobian(t,q,a);
  otherwise
    error(['Unknown flag ''' flag '''.']);
end
% 
function dq = f(t,q,a)
  dq = (-q+cos(t))/a;

%
function dfdy = jacobian(t,q,a)
  dfdy = -1/a;