diff --git a/ext/cIGraph.c b/ext/cIGraph.c
index c100316..94b66d2 100644
--- a/ext/cIGraph.c
+++ b/ext/cIGraph.c
@@ -198,6 +198,11 @@ void Init_igraph(){
   rb_define_const(cIGraph, "WEAK",   INT2NUM(1));
   rb_define_const(cIGraph, "STRONG", INT2NUM(2));  
 
+  rb_define_const(cIGraph, "ARBITRARY", INT2NUM(0));
+  rb_define_const(cIGraph, "MUTUAL",    INT2NUM(1));
+  rb_define_const(cIGraph, "EACH",      INT2NUM(0));
+  rb_define_const(cIGraph, "COLLAPSE",  INT2NUM(1));
+
   rb_define_method(cIGraph, "[]",            cIGraph_get_edge_attr, 2); /* in cIGraph_attribute_handler.c */
   rb_define_method(cIGraph, "[]=",           cIGraph_set_edge_attr, 3); /* in cIGraph_attribute_handler.c */
   rb_define_alias (cIGraph, "get_edge_attr", "[]");
@@ -269,9 +274,16 @@ void Init_igraph(){
   rb_define_method(cIGraph, "minimum_spanning_tree_unweighted", cIGraph_minimum_spanning_tree_unweighted, 0); /* in cIGraph_spanning.c */
   rb_define_method(cIGraph, "minimum_spanning_tree_prim",       cIGraph_minimum_spanning_tree_prim,       1); /* in cIGraph_spanning.c */
 
-  rb_define_method(cIGraph, "transitivity",          cIGraph_transitivity,          0);
-  rb_define_method(cIGraph, "transitivity_local",    cIGraph_transitivity_local,    1);
-  rb_define_method(cIGraph, "transitivity_avglocal", cIGraph_transitivity_avglocal, 0);
+  rb_define_method(cIGraph, "transitivity",          cIGraph_transitivity,          0); /* in cIGraph_transitivity.c */
+  rb_define_method(cIGraph, "transitivity_local",    cIGraph_transitivity_local,    1); /* in cIGraph_transitivity.c */
+  rb_define_method(cIGraph, "transitivity_avglocal", cIGraph_transitivity_avglocal, 0); /* in cIGraph_transitivity.c */
+
+  rb_define_method(cIGraph, "to_directed",   cIGraph_to_directed,   1); /* in cIGraph_direction.c */
+  rb_define_method(cIGraph, "to_undirected", cIGraph_to_undirected, 1); /* in cIGraph_direction.c */  
+
+  rb_define_method(cIGraph, "laplacian", cIGraph_laplacian, 1); /* in cIGraph_spectral.c */
+
+  rb_define_method(cIGraph, "coreness", cIGraph_coreness, 1); /* in cIGraph_kcores.c */
 
   rb_define_method(cIGraph, "topological_sorting", cIGraph_topological_sorting, 1); /* in cIGraph_topological_sort.c */
 
diff --git a/ext/cIGraph.h b/ext/cIGraph.h
index ce89b4c..1090d44 100644
--- a/ext/cIGraph.h
+++ b/ext/cIGraph.h
@@ -109,6 +109,16 @@ VALUE cIGraph_transitivity         (VALUE self);
 VALUE cIGraph_transitivity_local   (VALUE self, VALUE vs);
 VALUE cIGraph_transitivity_avglocal(VALUE self);
 
+//Directedness conversion
+VALUE cIGraph_to_directed  (VALUE self, VALUE mode);
+VALUE cIGraph_to_undirected(VALUE self, VALUE mode);
+
+//Spectral properties
+VALUE cIGraph_laplacian(VALUE self, VALUE mode);
+
+//K-Cores
+VALUE cIGraph_coreness(VALUE self, VALUE mode);
+
 //Topological sorting
 VALUE cIGraph_topological_sorting(VALUE self, VALUE mode);
 
diff --git a/ext/cIGraph_direction.c b/ext/cIGraph_direction.c
new file mode 100644
index 0000000..f34e17e
--- /dev/null
+++ b/ext/cIGraph_direction.c
@@ -0,0 +1,39 @@
+#include "igraph.h"
+#include "ruby.h"
+#include "cIGraph.h"
+
+/* call-seq:
+ *   graph.to_directed(mode)
+ *
+ * Converts the graph to a directed graph. 
+ */
+VALUE cIGraph_to_directed(VALUE self, VALUE mode){
+
+  igraph_t *graph;
+  igraph_neimode_t pmode = NUM2INT(mode);
+  int ret;
+
+  Data_Get_Struct(self, igraph_t, graph);
+  IGRAPH_CHECK(ret = igraph_to_directed(graph,pmode));
+
+  return INT2NUM(ret);
+
+}
+
+/* call-seq:
+ *   graph.to_undirected(mode)
+ *
+ * Converts the graph to a directed graph. 
+ */
+VALUE cIGraph_to_undirected(VALUE self, VALUE mode){
+
+  igraph_t *graph;
+  igraph_neimode_t pmode = NUM2INT(mode);
+  int ret;
+
+  Data_Get_Struct(self, igraph_t, graph);
+  IGRAPH_CHECK(ret = igraph_to_undirected(graph,pmode));
+
+  return INT2NUM(ret);
+
+}
diff --git a/ext/cIGraph_kcores.c b/ext/cIGraph_kcores.c
new file mode 100644
index 0000000..b96524d
--- /dev/null
+++ b/ext/cIGraph_kcores.c
@@ -0,0 +1,39 @@
+#include "igraph.h"
+#include "ruby.h"
+#include "cIGraph.h"
+
+/* call-seq:
+ *   graph.coreness(mode) -> Array
+ *
+ * Finding the coreness of the vertices in a network. The k-core of a 
+ * graph is a maximal subgraph in which each vertex has at least degree k.
+ * (Degree here means the degree in the subgraph of course.). The coreness 
+ * of a vertex is the highest order of a k-core containing the vertex.
+ *
+ * This function implements the algorithm presented in Vladimir Batagelj, 
+ * Matjaz Zaversnik: An O(m) Algorithm for Cores Decomposition of Networks. 
+ */
+VALUE cIGraph_coreness(VALUE self, VALUE mode){
+
+  igraph_t *graph;
+  igraph_neimode_t pmode = NUM2INT(mode);
+  igraph_vector_t cores;
+  int i;
+  VALUE result = rb_ary_new();
+  
+  Data_Get_Struct(self, igraph_t, graph);
+
+  //vector to hold the results of the calculations
+  igraph_vector_init(&cores,0);
+
+  igraph_coreness(graph,&cores,pmode);
+
+  for(i=0; i< igraph_vector_size(&cores); i++){
+    rb_ary_push(result,VECTOR(cores)[i]);
+  }
+
+  igraph_vector_destroy(&cores);
+
+  return result;
+
+}
diff --git a/ext/cIGraph_spectral.c b/ext/cIGraph_spectral.c
new file mode 100644
index 0000000..ddc1b01
--- /dev/null
+++ b/ext/cIGraph_spectral.c
@@ -0,0 +1,57 @@
+#include "igraph.h"
+#include "ruby.h"
+#include "cIGraph.h"
+
+/* call-seq:
+ *   graph.laplacian(mode) -> Array
+ *
+ *  Returns the Laplacian matrix of a graph
+ *
+ * The graph Laplacian matrix is similar to an adjacency matrix but 
+ * contains -1's instead of 1's and the vertex degrees are included 
+ * in the diagonal. So the result for edge i--j is -1 if i!=j and is 
+ * equal to the degree of vertex i if i==j. igraph_laplacian will work 
+ * on a directed graph (although this does not seem to make much sense) 
+ * and ignores loops.
+ *
+ * Mode is a boolean specifying whether the normalized version should be used
+ * The normalised Laplacian matrix has 1 in the diagonal 
+ * and -1/sqrt(d[i]d[j]) if there is an edge from i to j.
+ *
+ * The first version of this function was written by Vincent Matossian. 
+ */
+VALUE cIGraph_laplacian(VALUE self, VALUE mode){
+
+  igraph_t *graph;
+  igraph_bool_t pmode = 0;
+  igraph_matrix_t res;
+  int i;
+  int j;
+  VALUE row;
+  VALUE val;
+  VALUE matrix = rb_ary_new();
+
+  if(mode = Qtrue)
+    pmode = 1;
+
+  Data_Get_Struct(self, igraph_t, graph);
+
+  //matrix to hold the results of the calculations
+  igraph_matrix_init(&res,igraph_vcount(graph),igraph_vcount(graph));
+
+  IGRAPH_CHECK(igraph_laplacian(graph,&res,pmode));
+
+  for(i=0; i<igraph_matrix_nrow(&res); i++){
+    row = rb_ary_new();
+    rb_ary_push(matrix,row);
+    for(j=0; j<igraph_matrix_ncol(&res); j++){
+      val = rb_float_new(MATRIX(res,i,j));
+      rb_ary_push(row,val);
+    }
+  }
+
+  igraph_matrix_destroy(&res);
+
+  return matrix;
+
+}
diff --git a/ext/cIGraph_transtivity.c b/ext/cIGraph_transitivity.c
similarity index 100%
rename from ext/cIGraph_transtivity.c
rename to ext/cIGraph_transitivity.c
diff --git a/test/tc_cores.rb b/test/tc_cores.rb
new file mode 100644
index 0000000..7b4341e
--- /dev/null
+++ b/test/tc_cores.rb
@@ -0,0 +1,10 @@
+require 'test/unit'
+require 'igraph'
+
+class TestGraph < Test::Unit::TestCase
+  def test_coreness
+    g = IGraph.new(['A','B','C','D'],true)
+    c = g.coreness(IGraph::ALL)
+    assert_equal c.length, g.vcount
+  end
+end
diff --git a/test/tc_directedness.rb b/test/tc_directedness.rb
new file mode 100644
index 0000000..77ea106
--- /dev/null
+++ b/test/tc_directedness.rb
@@ -0,0 +1,31 @@
+require 'test/unit'
+require 'igraph'
+
+class TestGraph < Test::Unit::TestCase
+  def test_directed_conv
+
+    g = IGraph.new(['A','B','B','C','C','D'],false)
+
+    g.to_directed(IGraph::ARBITRARY)
+    assert g.are_connected?('A','B') || g.are_connected?('B','A')
+    assert !(g.are_connected?('A','B') && g.are_connected?('B','A'))
+
+    g = IGraph.new(['A','B','B','C','C','D'],false)
+
+    g.to_directed(IGraph::MUTUAL)
+    assert g.are_connected?('A','B') && g.are_connected?('B','A')
+
+  end
+  def test_undirected
+    g = IGraph.new(['A','B','B','A','B','C','C','D'],true)
+    
+    g.to_undirected(IGraph::EACH)
+    assert_equal 4, g.ecount
+
+    g = IGraph.new(['A','B','B','A','B','C','C','D'],true)
+    
+    g.to_undirected(IGraph::COLLAPSE)
+    assert_equal 3, g.ecount
+
+  end  
+end
diff --git a/test/tc_directedness.rb~ b/test/tc_directedness.rb~
new file mode 100644
index 0000000..1e1d7aa
--- /dev/null
+++ b/test/tc_directedness.rb~
@@ -0,0 +1,31 @@
+require 'test/unit'
+require 'igraph'
+
+class TestGraph < Test::Unit::TestCase
+  def test_directed
+
+    g = IGraph.new(['A','B','B','C','C','D'],false)
+
+    g.to_directed(IGraph::ARBITRARY)
+    assert g.are_connected?('A','B') || g.are_connected?('B','A')
+    assert !(g.are_connected?('A','B') && g.are_connected?('B','A'))
+
+    g = IGraph.new(['A','B','B','C','C','D'],false)
+
+    g.to_directed(IGraph::MUTUAL)
+    assert g.are_connected?('A','B') && g.are_connected?('B','A')
+
+  end
+  def test_undirected
+    g = IGraph.new(['A','B','B','A','B','C','C','D'],true)
+    
+    g.to_undirected(IGraph::EACH)
+    assert_equal 4, g.ecount
+
+    g = IGraph.new(['A','B','B','A','B','C','C','D'],true)
+    
+    g.to_undirected(IGraph::COLLAPSE)
+    assert_equal 3, g.ecount
+
+  end  
+end
diff --git a/test/tc_shortest_paths.rb~ b/test/tc_shortest_paths.rb~
new file mode 100644
index 0000000..0960ecd
--- /dev/null
+++ b/test/tc_shortest_paths.rb~
@@ -0,0 +1,44 @@
+require 'test/unit'
+require 'igraph'
+
+class TestGraph < Test::Unit::TestCase
+  def test_shortest_paths
+    graph = IGraph.new(['A','B','C','D'],true)
+    m = graph.shortest_paths(['A'],IGraph::ALL)
+    assert_equal 1, m[0][1]
+    assert_equal 0, m[0][0]
+    assert_equal graph.vcount, m[0].size
+    assert_equal nil, m[0][2]
+  end
+
+  def test_get_shortest_paths
+    graph = IGraph.new(['A','B','C','D'],true)    
+    m = graph.get_shortest_paths('A',['B'],IGraph::ALL)
+    assert_equal ['A','B'], m[0]
+    #assert_equal [],        m[1]
+  end
+
+  def test_get_all_shortest_paths
+    graph = IGraph.new(['A','B','A','C','B','D','C','D'],true)    
+    m = graph.get_all_shortest_paths('A',['D'],IGraph::ALL)
+    assert_equal 2, m.length
+  end
+
+  def test_average_path_length
+    graph = IGraph.new(['A','B','A','C','B','D','C','D'],true)    
+    m = graph.average_path_length(true,true)
+    assert_equal 1.2, m
+  end
+
+  def test_diameter_girth
+    graph = IGraph.new(['A','B','A','C','B','D'],true)    
+    m = graph.diameter(true,true)
+    assert_equal 3, m.length
+    assert_raises IGraphError do 
+      graph.girth
+    end
+    graph = IGraph.new(['A','B','A','C','B','D','C','D'],true)    
+    assert_equal 4, graph.girth.length
+  end
+
+end
diff --git a/test/tc_spanning.rb~ b/test/tc_spanning.rb~
new file mode 100644
index 0000000..3ca9f16
--- /dev/null
+++ b/test/tc_spanning.rb~
@@ -0,0 +1,33 @@
+require 'test/unit'
+require 'igraph'
+
+class TestGraph < Test::Unit::TestCase
+  def test_closeness
+    g = IGraph.new(['A','B','B','C','C','D'],true)
+    assert_equal [0.75], g.closeness(['B'],IGraph::ALL)
+  end
+  def test_betweenness
+    g = IGraph.new(['A','B','B','C','C','D'],true)
+    assert_equal [0,2], g.betweenness(['A','B'],true)
+  end
+  def test_edge_betweenness
+    g = IGraph.new(['A','B','C','D'],true)
+    assert_equal [1,1], g.edge_betweenness(true)
+  end    
+  def test_pagerank
+    g = IGraph.new(['A','B','C','D','E','B','F','B'],true)
+    assert_equal 67, (g.pagerank(['B'],true,100,0.01,0.8)[0] * 100).to_i
+  end 
+  def test_constraint
+    g = IGraph.new(['A','B','C','D'],true)
+    assert_equal [1], g.constraint(['A'])    
+    assert_raises IGraphError do
+      g.constraint(['A'],[3])    
+    end
+    assert_equal [1], g.constraint(['A'],[2,3])    
+  end
+  def test_maxdegree
+    g = IGraph.new(['A','B','C','D','A','E','A','F'],true)
+    assert_equal 3, g.maxdegree(g.vertices,IGraph::ALL,true)        
+  end
+end
diff --git a/test/tc_spectral.rb b/test/tc_spectral.rb
new file mode 100644
index 0000000..9080184
--- /dev/null
+++ b/test/tc_spectral.rb
@@ -0,0 +1,12 @@
+require 'test/unit'
+require 'igraph'
+
+class TestGraph < Test::Unit::TestCase
+  def test_laplacian
+    g = IGraph.new(['A','B','C','D'],false)
+    m = g.laplacian(false)
+    assert_equal m.length, g.vcount
+    m = g.laplacian(true)
+    assert_equal m.length, g.vcount
+  end
+end
diff --git a/test/tc_spectral.rb~ b/test/tc_spectral.rb~
new file mode 100644
index 0000000..cfd4a10
--- /dev/null
+++ b/test/tc_spectral.rb~
@@ -0,0 +1,12 @@
+require 'test/unit'
+require 'igraph'
+
+class TestGraph < Test::Unit::TestCase
+  def test_laplacian
+    g = IGraph.new(['A','B','C','D'],true)
+    m = g.laplacian(false)
+    p m
+    m = g.laplacian(true)
+    p m
+  end
+end
diff --git a/test/tc_thrash.rb b/test/tc_thrash.rb
new file mode 100644
index 0000000..b91222d
--- /dev/null
+++ b/test/tc_thrash.rb
@@ -0,0 +1,41 @@
+require 'test/unit'
+require 'igraph'
+
+class Array
+  def mean
+    total = 0.0
+    self.each do |i|
+      total += i
+    end
+    total / self.length.to_f
+  end
+end
+
+class TestGraph < Test::Unit::TestCase
+  def test_thrash
+    g = IGraph.new([],true)
+    v = 100
+    v.times do |x|
+      g.add_vertex(x)
+    end
+    200.times do |x|
+      g.add_edge(rand(v/2),rand(v/2))
+    end
+    200.times do |x|
+      g.add_edge(rand(v/2)+v/2,rand(v/2)+v/2)
+    end    
+    assert_equal v, g.vcount
+    h,i = g.decompose(IGraph::WEAK,-1,2)
+
+    p h.vcount
+    p i.vcount
+
+    p h.degree(h.to_a[20..30],IGraph::ALL,false).mean
+    p h.degree(h.to_a[10..20],IGraph::ALL,false).mean
+
+    p h.betweenness(h.to_a[20..30],true).mean
+    p h.betweenness(h.to_a[10..20],true).mean
+
+  end
+end
+ 
diff --git a/test/tc_thrash.rb~ b/test/tc_thrash.rb~
new file mode 100644
index 0000000..56c39a5
--- /dev/null
+++ b/test/tc_thrash.rb~
@@ -0,0 +1,13 @@
+require 'test/unit'
+require 'igraph'
+
+class TestGraph < Test::Unit::TestCase
+  def test_thrash
+    g = IGraph.new([],true)
+    10_000.times do |x|
+      g.add_vertex(x)
+    end
+    assert_equal 10_000, g.vcount
+  end
+end
+ 
diff --git a/test/tc_transitivity.rb~ b/test/tc_transitivity.rb~
new file mode 100644
index 0000000..d9b0805
--- /dev/null
+++ b/test/tc_transitivity.rb~
@@ -0,0 +1,25 @@
+require 'test/unit'
+require 'igraph'
+
+class TestGraph < Test::Unit::TestCase
+  def test_subcomponent
+    g = IGraph.new([1,2,3,4])
+    assert_equal [1,2], g.subcomponent(1,IGraph::ALL)
+  end
+  def test_subgraph
+    g = IGraph.new([1,2,3,4])
+    h = g.subgraph([1,2])
+    assert_equal 2, h.vcount
+    assert_equal [1,2], h.vertices
+  end
+  def test_clusters
+    g  = IGraph.new([1,2,3,4])
+    assert_equal 2, g.clusters(IGraph::WEAK).length
+    assert_equal [1,2], g.clusters(IGraph::WEAK)[0]
+  end
+  def test_decompose
+    g = IGraph.new([1,2,3,4])
+    assert_equal 2, g.decompose(IGraph::WEAK).length
+    assert_equal [1,2], g.decompose(IGraph::WEAK)[0].vertices
+  end
+end
diff --git a/test/test_all.rb b/test/test_all.rb
index 7597197..62a7fbe 100644
--- a/test/test_all.rb
+++ b/test/test_all.rb
@@ -12,12 +12,15 @@ require 'tc_basic_properties'
 require 'tc_centrality'
 require 'tc_components'
 require 'tc_copy'
+require 'tc_cores'
+require 'tc_directedness'
 require 'tc_error_handling'
 require 'tc_file_read_write'
 require 'tc_layout'
 require 'tc_matrix'
 require 'tc_shortest_paths'
 require 'tc_spanning'
+require 'tc_spectral'
 require 'tc_topological_sort'
 require 'tc_transitivity'
 require 'tc_vertex_neighbourhood'