diff --git a/thu_dsa/chp2/Vector.h b/thu_dsa/chp2/Vector.h
index 00b4f88..488bfee 100644
--- a/thu_dsa/chp2/Vector.h
+++ b/thu_dsa/chp2/Vector.h
@@ -34,6 +34,7 @@ public:
 	//constructors
 	Vector();
 	Vector(int capacity);
+	Vector(int size, T const &value);
 	Vector(T* const A, int n) { copyfrom(A, 0, n); }
 	Vector(T* const A, int lo, int hi) { copyfrom(A, lo, hi); }
 	Vector(Vector<T> const &V) { copyfrom(V._elem, 0, V._size); }
@@ -149,6 +150,15 @@ Vector<T>::Vector(int capacity) {
 	_elem = new T[_capacity];
 }
 
+template<typename T>
+Vector<T>::Vector(int size, T const &value){
+	_capacity = size << 1;
+	_size     = size;
+	_elem = new T[_capacity];
+	for (int ix = 0; ix != _size; ++ix)
+		_elem[ix] = value;
+}
+
 //read-only interfaces
 template<typename T>
 void Vector<T>::print() {
diff --git a/thu_dsa/chp2/testVector.cpp b/thu_dsa/chp2/testVector.cpp
index 30d9e1d..9eda077 100644
--- a/thu_dsa/chp2/testVector.cpp
+++ b/thu_dsa/chp2/testVector.cpp
@@ -66,6 +66,12 @@ void test_constructor() {
 	assert(V5.getSize() == 2);
 	assert(V5.getCapacity() == 4);
 
+	Vector<int> V6(10, 0);
+	assert(V6.getSize() == 10);
+	assert(V6.getCapacity() == 20);
+	for (int ix = 0; ix != 10; ++ix)
+		assert(V6[ix] == 0);
+
 	cout << "test passed." << endl;
 }
 
diff --git a/thu_dsa/chp6/Edge.h b/thu_dsa/chp6/Edge.h
index 16df902..4dc6a24 100644
--- a/thu_dsa/chp6/Edge.h
+++ b/thu_dsa/chp6/Edge.h
@@ -5,10 +5,12 @@
 
 template <typename Te>
 class Edge{
+public:
 	Te data;
 	double weight = 1;
 	Etype type    = UNDETERMINED;
 
+	Edge() = default;
 	Edge(Te data) : data(data) {}
 	Edge(Te data, double w) : data(data), weight(w) {}
 };
diff --git a/thu_dsa/chp6/Graph.h b/thu_dsa/chp6/Graph.h
index 36ac2f7..dd03498 100644
--- a/thu_dsa/chp6/Graph.h
+++ b/thu_dsa/chp6/Graph.h
@@ -8,7 +8,7 @@ typedef enum { UNDISCOVERED, DISCOVERED, VISITED } VStatus;
 typedef enum { UNDETERMINED, TREE, BACKWARD, FORWARD, CROSS } Etype;
 
 //abstract class Graph
-template <typename Tv> template <typename Te>
+template <typename Tv, typename Te>
 class Graph{
 private:
 	void reset();
@@ -38,11 +38,11 @@ public:
 
 	//directed egde methods
 	virtual bool exists(int, int) = 0;
-	virtual void insertEdge(Te const&, int, int, int) = 0;
+	virtual void insertEdge(Te const&, double, int, int) = 0;
 	virtual Te   removeEdge(int, int) = 0;
 	virtual Etype& type(int, int) = 0;
 	virtual Te& edge(int, int) = 0;
-	virtual int& weight(int, int) = 0;
+	virtual double& weight(int, int) = 0;
 
 	//Graph related algorithms
 	void bfs(int);
diff --git a/thu_dsa/chp6/GraphMatrix.h b/thu_dsa/chp6/GraphMatrix.h
index a7399a2..cd4a651 100644
--- a/thu_dsa/chp6/GraphMatrix.h
+++ b/thu_dsa/chp6/GraphMatrix.h
@@ -6,7 +6,7 @@
 #include "Vertex.h"
 #include "../chp2/Vector.h"
 
-template <typename Tv> template <typename Te>
+template <typename Tv, typename Te> 
 class GraphMatrix: public Graph<Tv, Te>{
 private:
 	Vector<Vertex<Tv>> V;
@@ -29,60 +29,83 @@ public:
 	int outDegree(int vertexId) { return V[vertexId].outDegree; }
 	int firstNeighbor(int vertexId);
 	int nextNeighbor(int vertexId, int curr);
-	int& dtime(int vertexId) { return V[vertexId].dtime; }
-	int& ftime(int vertexId) { return V[vertexId].ftime; }
+	int& dtime(int vertexId) { return V[vertexId].dTime; }
+	int& ftime(int vertexId) { return V[vertexId].fTime; }
 	int& parent(int vertexId) { return V[vertexId].parent; }
 	int& priority(int vertexId) { return V[vertexId].priority; }
 	VStatus& status(int vertexId) { return V[vertexId].status; }
 
 	//directed edge methods
 	bool exists(int src, int tail) { return E[src][tail] != nullptr; }
-	void insertEdge(Te const &data, int weight, int src, int tail);
+	void insertEdge(Te const &data, int src, int tail) { insertEdge(data, 1, src, tail); }
+	void insertEdge(Te const &data, double weight, int src, int tail);
 	Te   removeEdge(int src, int tail);
-	Etype& type(int src, int tail) { return E[src][tail]->type; }
-	Te&    edge(int src, int tail) { return E[src][tail]->data; }
-	int&   weight(int src, int tail) { return E[src][tail]->weight; }
+	Etype&  type(int src, int tail) { return E[src][tail]->type; }
+	Te&     edge(int src, int tail) { return E[src][tail]->data; }
+	double& weight(int src, int tail) { return E[src][tail]->weight; }
 };
 
+//application interfaces
+void graph_demo(GraphMatrix<char, int> &G);
+
 /*---------------Implementations---------------*/
 
 //constructor
-template <typename Tv> template <typename Te>
+template <typename Tv, typename Te>
 GraphMatrix<Tv, Te>::GraphMatrix(){
 	num_of_vertices = 0;
 	num_of_edges    = 0;
+}
 
-	V = Vector<Vertex<Tv>>();
-	E = Vector<Vector<Edge<Te>>>();
+//deconstructor
+template <typename Tv, typename Te>
+GraphMatrix<Tv, Te>::~GraphMatrix(){
+	for (int ix = 0; ix != num_of_vertices; ++ix)
+		for (int jx = 0; jx != num_of_vertices; ++jx)
+			if (exists(ix, jx)) delete E[ix][jx];
 }
 
 //implementations of abstract Graph methods
 
 //vertex methods
-template <typename Tv> template <typename Te>
+template <typename Tv, typename Te>
 int GraphMatrix<Tv, Te>::insertVertex(Tv const & data){
 	V.push_back(Vertex<Tv>(data));
 	for (int ix = 0; ix != num_of_vertices; ++ix) E[ix].push_back(nullptr);
-	E.push_back(Vector<Edge<Te>*>(nullptr, ++num_of_vertices));
+	E.push_back(Vector<Edge<Te>*>(++num_of_vertices, nullptr));
 	return num_of_vertices - 1;
 }
 
-template <typename Tv> template <typename Te>
-Te GraphMatrix<Tv, Te>::removeVertex(int vertexId){
+template <typename Tv, typename Te>
+Tv GraphMatrix<Tv, Te>::removeVertex(int vertexId){
+	for (int ix = 0; ix != num_of_vertices; ++ix)
+		if (exists(vertexId, ix)) removeEdge(vertexId, ix);
+
 	for (int ix = 0; ix != num_of_vertices; ++ix) {
-		//remove edges
-		if(exists(ix, vertexId) removeEdge(ix, vertexId);
-		if(exists(vertexId, ix) removeEdge(vertexId, ix);
+		if(exists(ix, vertexId))  removeEdge(ix, vertexId);
 		E[ix].pop(vertexId);
 	}
 	E.pop(vertexId);
-	--num_of_vertices;
+	num_of_vertices--;
 	return V.pop(vertexId).data;
 }
 
+template <typename Tv, typename Te>
+int GraphMatrix<Tv, Te>::firstNeighbor(int vertexId) {
+	return nextNeighbor(vertexId, num_of_vertices);
+}
+
+template <typename Tv, typename Te>
+int GraphMatrix<Tv, Te>::nextNeighbor(int vertexId, int curr) {
+	while(0 <= --curr){
+		if (exists(vertexId, curr)) break;
+	}
+	return curr;
+}
+
 //edge methods
-template <typename Tv> template <typename Te>
-void GraphMatrix<Tv, Te>::insertEdge(Te const &data, int weight, int src, int tail){
+template <typename Tv, typename Te>
+void GraphMatrix<Tv, Te>::insertEdge(Te const &data, double weight, int src, int tail){
 	if (src < 0 || src >= num_of_vertices || tail < 0 || tail >= num_of_vertices) return;
 	if (exists(src, tail)) return;
 
@@ -90,14 +113,14 @@ void GraphMatrix<Tv, Te>::insertEdge(Te const &data, int weight, int src, int ta
 
 	++num_of_edges;
 	V[tail].inDegree++;
-	V[src].outDegree--;
+	V[src].outDegree++;
 }
 
-template <typename Tv> template <typename Te>
+template <typename Tv, typename Te>
 Te GraphMatrix<Tv, Te>::removeEdge(int src, int tail){
 	Te edgeBak = edge(src, tail);
-	delete edge(src, tail);
-	edge(src, tail) = nullptr;
+	delete E[src][tail];
+	E[src][tail] = nullptr;
 
 	--num_of_edges;
 	V[tail].inDegree--;
@@ -105,4 +128,20 @@ Te GraphMatrix<Tv, Te>::removeEdge(int src, int tail){
 	return edgeBak;
 }
 
+//application interfaces
+void graph_demo(GraphMatrix<char, int> &G) {
+	G = GraphMatrix<char, int>();
+	char *alphabet = "abcdefghij";
+	for (int ix = 0; ix != 10; ++ix)
+		G.insertVertex(alphabet[ix]);
+	G.insertEdge(1, 0, 1);
+	G.insertEdge(1, 0, 7);
+	G.insertEdge(1, 4, 2);
+	G.insertEdge(1, 5, 4);
+	G.insertEdge(1, 5, 3);
+	G.insertEdge(1, 6, 7);
+	G.insertEdge(1, 9, 6);
+	G.insertEdge(1, 3, 8);
+}
+
 #endif
diff --git a/thu_dsa/chp6/Vertex.h b/thu_dsa/chp6/Vertex.h
index b3e024d..dce10ff 100644
--- a/thu_dsa/chp6/Vertex.h
+++ b/thu_dsa/chp6/Vertex.h
@@ -15,6 +15,7 @@ public:
 	int inDegree   = 0;
 	int outDegree  = 0;
 
+	Vertex() = default;
 	Vertex(Tv data) : data(data) {}
 };
 
diff --git a/thu_dsa/chp6/testGraphMatrix.cpp b/thu_dsa/chp6/testGraphMatrix.cpp
new file mode 100644
index 0000000..5cf8f6c
--- /dev/null
+++ b/thu_dsa/chp6/testGraphMatrix.cpp
@@ -0,0 +1,148 @@
+#include "GraphMatrix.h"
+#include <iostream>
+#include <cassert>
+using std::cout;
+using std::endl;
+
+void test_constructor();
+void test_vertex_insert();
+void test_vertex_delete();
+void test_edge_insert();
+
+int main(){
+	cout << "Running tests" << endl;
+
+	test_constructor();
+	test_vertex_insert();
+	test_edge_insert();
+	test_vertex_delete();
+
+	cout << "All tests passed." << endl;
+	system("pause");
+	return 0;
+}
+
+void test_constructor(){
+	GraphMatrix<int, int> G;
+	assert(G.num_of_edges == 0);
+	assert(G.num_of_vertices == 0);
+}
+
+void test_vertex_insert(){
+	GraphMatrix<char, int> G;
+	G.insertVertex('a');
+	assert(G.num_of_vertices == 1);
+	assert(G.num_of_edges == 0);
+	assert(G.exists(0, 0) == false);
+	assert(G.vertex(0) == 'a');
+	assert(G.inDegree(0) == 0);
+	assert(G.outDegree(0) == 0);
+	assert(G.priority(0) == 0);
+	assert(G.dtime(0) == -1);
+	assert(G.ftime(0) == -1);
+	assert(G.parent(0) == -1);
+
+	G.insertVertex('b');
+	assert(G.num_of_vertices == 2);
+	assert(G.num_of_edges == 0);
+	assert(G.exists(0, 1) == false);
+	assert(G.exists(1, 1) == false);
+	assert(G.vertex(1) == 'b');
+}
+
+void test_edge_insert(){
+	GraphMatrix<char, int> G;
+	graph_demo(G);
+
+	assert(G.num_of_edges == 8);
+	assert(G.edge(0, 1) == 1);
+	assert(G.weight(0, 1) == 1.);
+	assert(G.type(0, 1) == UNDETERMINED);
+	assert(G.exists(0, 7));
+	assert(G.exists(4, 2));
+	assert(G.exists(5, 4));
+	assert(G.exists(5, 3));
+	assert(G.exists(6, 7));
+	assert(G.exists(9, 6));
+	assert(G.exists(3, 8));
+
+	assert(!G.exists(1, 0));
+	assert(!G.exists(7, 0));
+	assert(!G.exists(2, 4));
+	assert(!G.exists(4, 5));
+	assert(!G.exists(3, 5));
+	assert(!G.exists(7, 6));
+	assert(!G.exists(6, 9));
+	assert(!G.exists(8, 3));
+
+	assert(G.inDegree(0) == 0);
+	assert(G.inDegree(1) == 1);
+	assert(G.inDegree(2) == 1);
+	assert(G.inDegree(3) == 1);
+	assert(G.inDegree(4) == 1);
+	assert(G.inDegree(5) == 0);
+	assert(G.inDegree(6) == 1);
+	assert(G.inDegree(7) == 2);
+	assert(G.inDegree(8) == 1);
+	assert(G.inDegree(9) == 0);
+
+	assert(G.outDegree(0) == 2);
+	assert(G.outDegree(1) == 0);
+	assert(G.outDegree(2) == 0);
+	assert(G.outDegree(3) == 1);
+	assert(G.outDegree(4) == 1);
+	assert(G.outDegree(5) == 2);
+	assert(G.outDegree(6) == 1);
+	assert(G.outDegree(7) == 0);
+	assert(G.outDegree(8) == 0);
+	assert(G.outDegree(9) == 1);
+}
+
+void test_vertex_delete(){
+	GraphMatrix<char, int> G;
+	graph_demo(G);
+
+	G.removeVertex(0);
+	assert(G.num_of_vertices == 9);
+	assert(G.num_of_edges == 6);
+	assert(G.inDegree(0) == 0);
+	assert(G.inDegree(1) == 1);
+	assert(G.inDegree(2) == 1);
+	assert(G.inDegree(3) == 1);
+	assert(G.inDegree(4) == 0);
+	assert(G.inDegree(5) == 1);
+	assert(G.inDegree(6) == 1);
+	assert(G.inDegree(7) == 1);
+	assert(G.inDegree(8) == 0);
+
+	assert(G.outDegree(0) == 0);
+	assert(G.outDegree(1) == 0);
+	assert(G.outDegree(2) == 1);
+	assert(G.outDegree(3) == 1);
+	assert(G.outDegree(4) == 2);
+	assert(G.outDegree(5) == 1);
+	assert(G.outDegree(6) == 0);
+	assert(G.outDegree(7) == 0);
+	assert(G.outDegree(8) == 1);
+	
+	G.removeVertex(5);
+	assert(G.num_of_vertices == 8);
+	assert(G.num_of_edges == 4);
+	assert(G.inDegree(0) == 0);
+	assert(G.inDegree(1) == 1);
+	assert(G.inDegree(2) == 1);
+	assert(G.inDegree(3) == 1);
+	assert(G.inDegree(4) == 0);
+	assert(G.inDegree(5) == 0);
+	assert(G.inDegree(6) == 1);
+	assert(G.inDegree(7) == 0);
+
+	assert(G.outDegree(0) == 0);
+	assert(G.outDegree(1) == 0);
+	assert(G.outDegree(2) == 1);
+	assert(G.outDegree(3) == 1);
+	assert(G.outDegree(4) == 2);
+	assert(G.outDegree(5) == 0);
+	assert(G.outDegree(6) == 0);
+	assert(G.outDegree(7) == 0);
+}