This function links the user's choice of transformation with the associated numpy function

def transform_define(transform):
        """
        This function links the user's choice of transformation with the associated numpy function
        """
        if transform == 'tanh':
            return np.tanh
        elif transform == 'exp':
            return np.exp
        elif transform == 'logit':
            return Family.ilogit
        elif transform is None:
            return np.array
        else:
            return None