'(str) BLAS prefix of currently active representation matrices'

@property
def prefix(self):

    arrays = (self._design, self._obs_intercept, self._obs_cov, self._transition, self._state_intercept, self._selection, self._state_cov)
    if (self.endog is not None):
        arrays = ((self.endog,) + arrays)
    return find_best_blas_type(arrays)[0]
