diff --git a/atpg b/atpg
index fcca67d..cb4983c 100755
Binary files a/atpg and b/atpg differ
diff --git a/circuit.cpp b/circuit.cpp
index 8dea274..6ad6907 100644
--- a/circuit.cpp
+++ b/circuit.cpp
@@ -3,7 +3,19 @@
 #include <queue>
 #include <unordered_map>
 
-void Circuit::cal_topo_index() {
+
+void Circuit::init_stems() {
+    for(auto& gate: gates) {
+        if(gate->outputs.size() >= 2) {
+            stems.push_back(gate);
+        }
+    }
+    for(auto &gate :  PIs) {
+        stems.push_back(gate);
+    }
+}
+
+void Circuit::init_topo_index() {
     int topo = 1;
     std::queue<Gate*> q;
 
@@ -80,4 +92,6 @@ int Circuit::cal_gate_value(const Gate* &gate) {
             break;
     }
     return res;
-}
\ No newline at end of file
+}
+
+
diff --git a/circuit.h b/circuit.h
index 64d4ff7..7748f0b 100644
--- a/circuit.h
+++ b/circuit.h
@@ -14,14 +14,31 @@ public:
     std::vector<Gate*> inputs;
 };
 
+class Fault {
+public:
+    Gate* gate;
+    enum Type { SA0, SA1 } type;
+    Fault(Gate* gate, Type type):gate(gate),type(type) {}
+};
+
 class Circuit {
 public:
 std::vector<Gate*> PIs;
 std::vector<Gate*> POs;
 std::vector<Gate*> gates;
+std::vector<Gate*> stems;// PI + stems
+
 std::unordered_map<std::string, Gate*> name2gate;
 void parse_from_file(const char *filename);
 int cal_gate_value(const Gate* &gate);
-void cal_topo_index();
+void init_topo_index();
+void init_stems();
+
+// local search
+std::vector<int> local_search(const std::vector<Fault*> &faults);
+
+void ls_init_circuit();
+void ls_init_vector(std::vector<Gate*> *vec);
+
 
 };
\ No newline at end of file
diff --git a/ls.cpp b/ls.cpp
index 0471d53..8b09a4f 100644
--- a/ls.cpp
+++ b/ls.cpp
@@ -1,35 +1,17 @@
-#include "ls.h"
+#include "circuit.h"
 
-
-std::vector<int> local_search(Circuit* circuit) {
+std::vector<int> Circuit::local_search(const std::vector<Fault*> &faults) {
 
     // local search vector
-    std::vector<Gate*> vec;
-
-    init_vector(circuit, &vec);
-
-    init_circuit(circuit);
+    ls_init_circuit();
     
     printf("local search!\n");
 
     return std::vector<int>();
 }
 
-
-void init_circuit(Circuit* circuit) {
-    for(auto pi : circuit->PIs) {
+void Circuit::ls_init_circuit() {
+    for(auto pi : PIs) {
         pi->value = rand() % 2;
     }
-}
-
-void init_vector(Circuit* circuit, std::vector<Gate*> *vec) {
-    for(auto pi : circuit->PIs) {
-        vec->push_back(pi);
-    }
-    for(auto gate : circuit->gates) {
-        // fanout stem
-        if(gate->outputs.size() >= 2) {
-            vec->push_back(gate);
-        }
-    }
 }
\ No newline at end of file
diff --git a/ls.h b/ls.h
deleted file mode 100644
index 270c45c..0000000
--- a/ls.h
+++ /dev/null
@@ -1,9 +0,0 @@
-#pragma once
-
-#include "circuit.h"
-
-std::vector<int> local_search(Circuit* circuit);
-
-// private
-void init_circuit(Circuit* circuit);
-void init_vector(Circuit* circuit, std::vector<Gate*> *vec);
\ No newline at end of file
diff --git a/main.cpp b/main.cpp
index 9954451..ba86ac3 100644
--- a/main.cpp
+++ b/main.cpp
@@ -3,7 +3,6 @@
 #include <assert.h>
 
 #include "circuit.h"
-#include "ls.h"
 
 int main(int args, char* argv[]) {
 
@@ -12,31 +11,32 @@ int main(int args, char* argv[]) {
         exit(1);
     }
 
+    srand(19260817);
+
     Circuit circuit;
 
-    printf("parsing file %s...\n", argv[1]);
+    printf("parsing file %s ...", argv[1]);
     circuit.parse_from_file(argv[1]);
+    circuit.init_stems();
+    circuit.init_topo_index();
+    printf(" Done.\n");
+
     printf("====== Circuit Statistics ====== \n");
     printf("PI:\t%ld\n", circuit.PIs.size());
     printf("PO:\t%ld\n", circuit.POs.size());
-    printf("Gates:\t%ld\n", circuit.name2gate.size());
+    printf("Gate:\t%ld\n", circuit.name2gate.size());
+    printf("Stem:\t%ld\n", circuit.stems.size());
+    printf("================================ \n");
 
-    int cnt = 0;
-    for(auto& gate: circuit.gates) {
-        if(gate->outputs.size() > 2) {
-            cnt++;
-        }
-    }
-    printf("Stem:\t%d\n", cnt);
+    std::vector<Fault*> faults;
 
-    printf("cal topo index ...\n");
-    circuit.cal_topo_index();
-    for(Gate* gate : circuit.gates) {
-        assert(gate->topo > 0);
+    // init faults
+    for(auto stem : circuit.stems) {
+        faults.push_back(new Fault(stem, Fault::SA0));
+        faults.push_back(new Fault(stem, Fault::SA1));
     }
 
-    srand(19260817);
-    local_search(&circuit);
+    auto pattern = circuit.local_search(faults);
 
     return 0;
 }
\ No newline at end of file