simplify memory tricks with pp object. include algebra tests in ancillaries_theta (commented out). don't need to recompute lik_fn_ff every eval_particle because f doesn't change inside slice sampling algo in the case of surrogate data method.
simplify memory tricks with pp object. include algebra tests in ancillaries_theta (commented out). don't need to recompute lik_fn_ff every eval_particle because f doesn't change inside slice sampling algo in the case of surrogate data method.

sebastien-bratieres/pygpstruct,sebastien-bratieres/pygpstruct