'obtain the probability array given an array of parameters
This is the function that can be called by loglike or other methods
that need the probabilities as function of the params.
Parameters
params : 1d array, (nparams,)
coefficients and tau that parameterize the model. The required
length can be obtained by nparams. (and will depend on the number
of degenerate leaves - not yet)
Returns
probs : array, (nobs, nchoices)
probabilites for all choices for each observation. The order
is available by attribute leaves. See note in docstring of class'

def get_probs(self, params):

    self.recursionparams = params
    self.calc_prob(self.tree)
    probs_array = np.array([self.probs[leaf] for leaf in self.leaves])
    return probs_array
