Constant prior of strength alpha.

    Prior is defined via

        b_ij=alpha for all i,j

    Parameters
    ----------
    C : (M, M) ndarray or scipy.sparse matrix
        Count matrix
    alpha : float (optional)
        Value of prior counts

    Returns
    -------
    B : (M, M) ndarray
        Prior count matrix

def prior_const(C, alpha=0.001):
    """Constant prior of strength alpha.

    Prior is defined via

        b_ij=alpha for all i,j

    Parameters
    ----------
    C : (M, M) ndarray or scipy.sparse matrix
        Count matrix
    alpha : float (optional)
        Value of prior counts

    Returns
    -------
    B : (M, M) ndarray
        Prior count matrix

    """
    B = alpha * np.ones(C.shape)
    return B