'ddt : discrete delta t
not tested yet'

def exactprocess(self, nobs, xzero=None, ddt=1.0, nrepl=2):

    if (xzero is None):
        xzero = self.xzero
    t = np.linspace(ddt, (nobs * ddt), nobs)
    normrvs = np.random.normal(size=(nrepl, nobs))
    inc = (self._drift + ((self._sigma * np.sqrt(ddt)) * normrvs))
    return (xzero + np.cumsum(inc, 1))
