diff --git a/src/mcsat/nra/nra_plugin.c b/src/mcsat/nra/nra_plugin.c index 6acdc476..7bdbb6a9 100644 --- a/src/mcsat/nra/nra_plugin.c +++ b/src/mcsat/nra/nra_plugin.c @@ -814,13 +814,39 @@ void nra_plugin_process_unit_constraint(nra_plugin_t* nra, trail_token_t* prop, } nra->ctx->hint_next_decision(nra->ctx, x); } - } else if (lp_feasibility_set_is_point_int(feasible_set)) { - // hint integer (also real) variable; + } else if (x_is_int_var && lp_feasibility_set_is_point_int(feasible_set)) { + // hint integer variable; // a good candidate for next decision as the feasibility set contains a single integer solution if (ctx_trace_enabled(nra->ctx, "nra::propagate")) { ctx_trace_printf(nra->ctx, "nra: hinting variable = %d\n", x); } nra->ctx->hint_next_decision(nra->ctx, x); + } else if (!lp_feasibility_set_is_full(feasible_set)) { + lp_interval_t x_interval; + lp_interval_construct_full(&x_interval); // [-inf, +inf] + // now we over-approx the feasible set using an interval and + // the result is stored in x_interval, e.g., [1.6, 2.5] + // union [4.2, 4.6] is approximated by [1.6, 4.6]. + feasible_set_db_approximate_value(nra->feasible_set_db, x, &x_interval); + int interval_dist = lp_interval_size_approx(&x_interval); + if (interval_dist <= 1) { + // interval distance of an interval [a, b] is defined as log2(|b - a|) + 1. + // interval distance 1 means that the absolute log2 distance + // between the upper and lower bound is 1. + // Consider the the interval [3,4], the interval distance is 1, and has + // two integer value: 3 and 4. + // Now consider the interval [5.5, 6.1], the interval distance is 0 and + // has one integer value: 6. log2(.6) = log2(6) - log2(10). + // Here, we are hinting to the main mcsat solver to decide on this variable + // as the possible integer values for the variable is highly likely one. + if (lp_value_is_integer(&x_value)) { + // it is good idea to decide on this variable (integers or reals) + if (ctx_trace_enabled(nra->ctx, "nra::propagate")) { + ctx_trace_printf(nra->ctx, "nra: hinting variable = %d\n", x); + } + nra->ctx->hint_next_decision(nra->ctx, x); + } + } } } lp_value_destruct(&x_value);