'Analyze impulse responses to shocks in system
Parameters
periods : int
var_decomp : ndarray (k x k), lower triangular
Must satisfy Omega = P P\', where P is the passed matrix. Defaults to
Cholesky decomposition of Omega
var_order : sequence
Alternate variable order for Cholesky decomposition
Returns
irf : IRAnalysis'

def irf(self, periods=10, var_decomp=None, var_order=None):

    if (var_order is not None):
        raise NotImplementedError('alternate    variable    order    not    implemented    (yet)')
    return IRAnalysis(self, P=var_decomp, periods=periods)
