function [theta,time] = partial(t_0,vel)
error    = .0001;
time     = t_0+.5;
theta    = atan(2);

fname     = 'fx';
test_name = 'check';

fc   = feval(fname,theta,time,t_0,vel);
test = feval(test_name,theta,time,t_0,vel);

while (abs(test(1,1)) > error | abs(test(2,1)) > error) 

  time  = fc(1,1) + time;
  theta = fc(2,1) + theta;
  test  = feval(test_name,theta,time,t_0,vel);
  
  fc  = feval(fname,theta,time,t_0,vel);

end
