diff --git a/atpg b/atpg
index 2ad58e5..dd5ffcb 100755
Binary files a/atpg and b/atpg differ
diff --git a/circuit.h b/circuit.h
index 6861c88..011261b 100644
--- a/circuit.h
+++ b/circuit.h
@@ -80,18 +80,18 @@ void init_stems();
 // local search
 
 // shared info
-static const int STEM_INC = 10;
+static const int STEM_INC = 2;
 static const int STEM_COST_MAX = 1e9;
 static ll stem_total_cost;
 static int stem_falsified_cnt;
 
-static const int PROPAGATE_INC = 10;
+static const int PROPAGATE_INC = 2;
 static const int PROPAGATE_COST_MAX = 1e9;
 static ll propagate_total_cost;
 static int propagate_falsified_cnt;
 
 static const int FAULT_INC = 1;
-static const int FAULT_COST_MAX = 20;
+static const int FAULT_COST_MAX = 1e9;
 static ll fault_total_cost;
 static int fault_falsified_cnt;
 
@@ -116,4 +116,8 @@ void ls_update(Gate* stem);
 ll ls_pick_score(Gate* stem, bool value, bool propagate);
 
 ll ls_score();
+
+
+// simulator
+int** simulate();
 };
\ No newline at end of file
diff --git a/ls.cpp b/ls.cpp
index 05df9ef..94e733a 100644
--- a/ls.cpp
+++ b/ls.cpp
@@ -28,6 +28,19 @@ bool Circuit::local_search(std::unordered_set<Fault*> &faults) {
             ls_update_weight();
             picked_stem = ls_pick_falsified_var(value, propagate);
             printf("[UP] propagate: %lld, stem: %lld, fault:%lld. propagate_cnt: %d, stem_cnt: %d, fault_cnt:%d\n", propagate_total_cost, stem_total_cost, fault_total_cost, propagate_falsified_cnt, stem_falsified_cnt, fault_falsified_cnt);
+
+            int** sa = simulate();
+            int cnt = 0;
+            static int max_cnt = 0;
+
+            for(Fault* f : faults) {
+                if(sa[f->gate->id][f->type]) {
+                    cnt++;
+                }
+            }
+            max_cnt = std::max(max_cnt, cnt);
+            
+            printf("[SOL] detect-faults: %d max-faults: %d\n", cnt, max_cnt);
         } else {
             // printf("pick: %s value: %d propagate: %d\n", picked_stem->name.c_str(), value, propagate);
             // printf("[LS] propagate: %lld, stem: %lld, fault:%lld. propagate_cnt: %d, stem_cnt: %d, fault_cnt:%d\n", propagate_total_cost, stem_total_cost, fault_total_cost, propagate_falsified_cnt, stem_falsified_cnt, fault_falsified_cnt);
diff --git a/simulator.cpp b/simulator.cpp
new file mode 100644
index 0000000..5fd4cad
--- /dev/null
+++ b/simulator.cpp
@@ -0,0 +1,150 @@
+#include "circuit.h"
+
+#include <assert.h>
+#include <unordered_map>
+
+int cal_value(Gate *g, int *value) {
+    int res;
+
+    switch(g->type) {
+        case Gate::NOT:
+            res = !value[g->inputs[0]->id];
+            break;
+        case Gate::BUF:
+            res = value[g->inputs[0]->id];
+            break;
+        case Gate::AND:
+            res = value[g->inputs[0]->id];
+            for(int i=1; i<g->inputs.size(); i++) {
+                res &= value[g->inputs[i]->id];
+            }
+            break;
+        case Gate::NAND:
+            res = value[g->inputs[0]->id];
+            for(int i=1; i<g->inputs.size(); i++) {
+                res &= value[g->inputs[i]->id];
+            }
+            res = !res;
+            break;
+        case Gate::OR:
+            res = value[g->inputs[0]->id];
+            for(int i=1; i<g->inputs.size(); i++) {
+                res |= value[g->inputs[i]->id];
+            }
+            break;
+        case Gate::NOR:
+            res = value[g->inputs[0]->id];
+            for(int i=1; i<g->inputs.size(); i++) {
+                res |= value[g->inputs[i]->id];
+            }
+            res = !res;
+            break;
+        case Gate::XOR:
+            res = value[g->inputs[0]->id];
+            for(int i=1; i<g->inputs.size(); i++) {
+                res ^= value[g->inputs[i]->id];
+            }
+            break;
+        case Gate::XNOR:
+            res = value[g->inputs[0]->id];
+            for(int i=1; i<g->inputs.size(); i++) {
+                res ^= value[g->inputs[i]->id];
+            }
+            res = !res;
+            break;
+        case Gate::INPUT:
+            res = value[g->id];
+            break;
+        default:
+            assert(false);
+            break;
+    }
+    return res;
+}
+
+bool cal_sa(Gate* g, bool x, int** sa, int *value) {
+    if(g->po) {
+        if(x == 0) return value[g->id];
+        else return !value[g->id];
+    }
+
+    bool sa0 = 0;
+    bool sa1 = 0;
+
+    for(Gate* out : g->outputs) {
+        if(!sa[out->id][0] && !sa[out->id][1]) continue;
+
+        if(cal_value(out, value) != value[out->id]) continue;
+
+        value[g->id] = !value[g->id];
+        bool detect = cal_value(out, value) != value[out->id];
+        value[g->id] = !value[g->id];
+        if(!detect) continue;
+
+        sa0 |= value[g->id];
+        sa1 |= !value[g->id];
+    }
+    if(x == 0) return sa0;
+    else return sa1;
+}
+
+
+int** Circuit::simulate() {
+
+    static bool init = false;
+    static int** sa = nullptr;
+    static int* value = nullptr;
+
+    if(!init) {
+        const int MAXN = gates.size() + 1;
+        init = true;
+        sa = new int*[MAXN];
+        for(int i=0; i<MAXN; i++) {
+            sa[i] = new int[2];
+        }
+        value = new int[MAXN];
+    }
+
+    // init PI
+    for(Gate* pi : PIs) {
+        value[pi->id] = pi->value;
+    }
+
+    for(Gate *g : gates) {
+        if(g->pi) continue;
+        value[g->id] = cal_value(g, value);
+    }
+
+    for(Gate *g : gates) {
+        assert(value[g->id] == cal_value(g, value));
+    }
+
+    std::queue<Gate*> q;
+    std::unordered_map<Gate*, int> topo;
+
+    // init PO
+    for(Gate* po : POs) {
+        sa[po->id][!value[po->id]] = 1;
+        sa[po->id][value[po->id]] = 0;
+        q.push(po);
+    }
+
+    while(!q.empty()) {
+        Gate* g = q.front();
+        q.pop();
+        for(Gate* in : g->inputs) {
+            if(++topo[in] == in->outputs.size()) {
+                sa[in->id][0] = cal_sa(in, 0, sa, value);
+                sa[in->id][1] = cal_sa(in, 1, sa, value);
+                q.push(in);
+            }
+        }
+    }
+
+    for(Gate* g : gates) {
+        assert(sa[g->id][0] == cal_sa(g, 0, sa, value));
+        assert(sa[g->id][1] == cal_sa(g, 1, sa, value));
+    }
+
+    return sa;
+}
\ No newline at end of file