<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def partial_fit(self, X):
 """ incrementally update the estimates Parameters X: array, list of arrays, PyEMMA reader input data. """

        from pyemma.coordinates import source

        self._estimate(source(X), partial_fit=True)
        self._estimated = True

        return self