diff --git a/src/adaptors/rotmat.rs b/src/adaptors/rotmat.rs
index 0c033ddd..540cf78c 100644
--- a/src/adaptors/rotmat.rs
+++ b/src/adaptors/rotmat.rs
@@ -19,40 +19,38 @@ use vec::Vec3;
 pub struct Rotmat<M>
 { priv submat: M }
 
-impl<M: Copy> Rotmat<M>
+impl<M: Clone> Rotmat<M>
 {
   pub fn submat(&self) -> M
-  { copy self.submat }
+  { self.submat.clone() }
 }
 
-pub fn rotmat2<N: Copy + Trigonometric + Neg<N>>(angle: N) -> Rotmat<Mat2<N>>
+pub fn rotmat2<N: Clone + Trigonometric + Neg<N>>(angle: N) -> Rotmat<Mat2<N>>
 {
-  let coa = angle.cos();
-  let sia = angle.sin();
+  let (sia, coa) = angle.sin_cos();
 
   Rotmat
-  { submat: Mat2::new( [ copy coa, -sia, copy sia, copy coa ] ) }
+  { submat: Mat2::new( [ coa.clone(), -sia, sia.clone(), coa ] ) }
 }
 
-pub fn rotmat3<N: Copy + Trigonometric + DivisionRing + Algebraic>
+pub fn rotmat3<N: Clone + Copy + Trigonometric + DivisionRing + Algebraic>
 (axisangle: Vec3<N>) -> Rotmat<Mat3<N>>
 {
   if axisangle.sqnorm().is_zero()
   { One::one() }
   else
   {
-    let mut axis  = axisangle;
-    let angle     = axis.normalize();
-    let _1        = One::one::<N>();
-    let ux        = copy axis.at[0];
-    let uy        = copy axis.at[1];
-    let uz        = copy axis.at[2];
-    let sqx       = ux * ux;
-    let sqy       = uy * uy;
-    let sqz       = uz * uz;
-    let cos       = angle.cos();
-    let one_m_cos = _1 - cos;
-    let sin       = angle.sin();
+    let mut axis   = axisangle;
+    let angle      = axis.normalize();
+    let _1         = One::one::<N>();
+    let ux         = axis.at[0].clone();
+    let uy         = axis.at[1].clone();
+    let uz         = axis.at[2].clone();
+    let sqx        = ux * ux;
+    let sqy        = uy * uy;
+    let sqz        = uz * uz;
+    let (sin, cos) = angle.sin_cos();
+    let one_m_cos  = _1 - cos;
 
     Rotmat {
       submat: Mat3::new( [
@@ -71,12 +69,12 @@ pub fn rotmat3<N: Copy + Trigonometric + DivisionRing + Algebraic>
   }
 }
 
-impl<N: Trigonometric + DivisionRing + Copy>
+impl<N: Trigonometric + DivisionRing + Clone>
 Rotation<Vec1<N>> for Rotmat<Mat2<N>>
 {
   #[inline]
   fn rotation(&self) -> Vec1<N>
-  { Vec1::new([ -(self.submat.at((0, 1)) / self.submat.at((0, 0))).atan() ]) }
+  { Vec1::new([ (-self.submat.at((0, 1))).atan2(&self.submat.at((0, 0))) ]) }
 
   #[inline]
   fn inv_rotation(&self) -> Vec1<N>
@@ -87,15 +85,15 @@ Rotation<Vec1<N>> for Rotmat<Mat2<N>>
   { *self = self.rotated(rot) }
 }
 
-impl<N: Trigonometric + DivisionRing + Copy>
+impl<N: Trigonometric + DivisionRing + Clone>
 Rotatable<Vec1<N>, Rotmat<Mat2<N>>> for Rotmat<Mat2<N>>
 {
   #[inline]
   fn rotated(&self, rot: &Vec1<N>) -> Rotmat<Mat2<N>>
-  { rotmat2(copy rot.at[0]) * *self }
+  { rotmat2(rot.at[0].clone()) * *self }
 }
 
-impl<N: Copy + Trigonometric + DivisionRing + Algebraic>
+impl<N: Clone + Copy + Trigonometric + DivisionRing + Algebraic>
 Rotation<Vec3<N>> for Rotmat<Mat3<N>>
 {
   #[inline]
@@ -112,15 +110,15 @@ Rotation<Vec3<N>> for Rotmat<Mat3<N>>
   { *self = self.rotated(rot) }
 }
 
-impl<N: Copy + Trigonometric + DivisionRing + Algebraic>
+impl<N: Clone + Copy + Trigonometric + DivisionRing + Algebraic>
 Rotatable<Vec3<N>, Rotmat<Mat3<N>>> for Rotmat<Mat3<N>>
 {
   #[inline]
   fn rotated(&self, axisangle: &Vec3<N>) -> Rotmat<Mat3<N>>
-  { rotmat3(copy *axisangle) * *self }
+  { rotmat3(axisangle.clone()) * *self }
 }
 
-impl<N: Copy + Rand + Trigonometric + Neg<N>> Rand for Rotmat<Mat2<N>>
+impl<N: Clone + Rand + Trigonometric + Neg<N>> Rand for Rotmat<Mat2<N>>
 {
   #[inline]
   fn rand<R: Rng>(rng: &mut R) -> Rotmat<Mat2<N>>
@@ -149,7 +147,7 @@ impl<M: RMul<V> + LMul<V>, V> Transform<V> for Rotmat<M>
   { self.inv_rotate(v) }
 }
 
-impl<N: Copy + Rand + Trigonometric + DivisionRing + Algebraic>
+impl<N: Clone + Copy + Rand + Trigonometric + DivisionRing + Algebraic>
 Rand for Rotmat<Mat3<N>>
 {
   #[inline]
@@ -195,12 +193,16 @@ impl<V, M: LMul<V>> LMul<V> for Rotmat<M>
 impl<M: Transpose> Inv for Rotmat<M>
 {
   #[inline]
-  fn invert(&mut self)
-  { self.transpose() }
+  fn invert(&mut self) -> bool
+  {
+    self.transpose();
+
+    true
+  }
 
   #[inline]
-  fn inverse(&self) -> Rotmat<M>
-  { self.transposed() }
+  fn inverse(&self) -> Option<Rotmat<M>>
+  { Some(self.transposed()) }
 }
 
 impl<M: Transpose>
diff --git a/src/adaptors/transform.rs b/src/adaptors/transform.rs
index 01564d3a..d3fd3857 100644
--- a/src/adaptors/transform.rs
+++ b/src/adaptors/transform.rs
@@ -179,7 +179,14 @@ Transformation<Transform<M, V>> for Transform<M, V>
   { copy *self }
 
   fn inv_transformation(&self) -> Transform<M, V>
-  { self.inverse() }
+  {
+    // FIXME: fail or return a Some<Transform<M, V>> ?
+    match self.inverse()
+    {
+      Some(t) => t,
+      None    => fail!("This transformation was not inversible.")
+    }
+  }
 
   fn transform_by(&mut self, other: &Transform<M, V>)
   { *self = other * *self; }
@@ -211,20 +218,26 @@ impl<M: Copy + Inv + RMul<V>, V: Copy + Neg<V>>
 Inv for Transform<M, V>
 {
   #[inline]
-  fn invert(&mut self)
+  fn invert(&mut self) -> bool
   {
-    self.submat.invert();
-    self.subtrans = self.submat.rmul(&-self.subtrans);
+    if !self.submat.invert()
+    { false }
+    else
+    {
+      self.subtrans = self.submat.rmul(&-self.subtrans);
+      true
+    }
   }
 
   #[inline]
-  fn inverse(&self) -> Transform<M, V>
+  fn inverse(&self) -> Option<Transform<M, V>>
   {
     let mut res = copy *self;
 
-    res.invert();
-
-    res
+    if res.invert()
+    { Some(res) }
+    else
+    { None }
   }
 }
 
diff --git a/src/dmat.rs b/src/dmat.rs
index db5d11a1..ebe7f2cf 100644
--- a/src/dmat.rs
+++ b/src/dmat.rs
@@ -137,16 +137,17 @@ impl<N: Copy + Eq + DivisionRing>
 Inv for DMat<N>
 {
   #[inline]
-  fn inverse(&self) -> DMat<N>
+  fn inverse(&self) -> Option<DMat<N>>
   {
     let mut res : DMat<N> = copy *self;
 
-    res.invert();
-
-    res
+    if res.invert()
+    { Some(res) }
+    else
+    { None }
   }
 
-  fn invert(&mut self)
+  fn invert(&mut self) -> bool
   {
     let     dim = self.dim;
     let mut res = one_mat_with_dim::<N>(dim);
@@ -169,7 +170,8 @@ Inv for DMat<N>
         n0 = n0 + 1;
       }
 
-      assert!(n0 != dim); // non inversible matrix
+      if n0 == dim
+      { return false }
 
       // swap pivot line
       if n0 != k
@@ -220,6 +222,8 @@ Inv for DMat<N>
     }
 
     *self = res;
+
+    true
   }
 }
 
diff --git a/src/mat.rs b/src/mat.rs
index 4fe5ef7d..2cf6b695 100644
--- a/src/mat.rs
+++ b/src/mat.rs
@@ -22,6 +22,7 @@ mod mat_impl;
 pub struct Mat1<N>
 { mij: [N, ..1 * 1] }
 
+clone_impl!(Mat1)
 mat_impl!(Mat1, 1)
 one_impl!(Mat1, [ _1 ])
 zero_impl!(Mat1, [ _0 ])
@@ -43,6 +44,7 @@ column_impl!(Mat1, 1)
 pub struct Mat2<N>
 { mij: [N, ..2 * 2] }
 
+clone_impl!(Mat2)
 mat_impl!(Mat2, 2)
 one_impl!(Mat2, [ _1 | _0 |
                   _0 | _1 ])
@@ -67,6 +69,7 @@ column_impl!(Mat2, 2)
 pub struct Mat3<N>
 { mij: [N, ..3 * 3] }
 
+clone_impl!(Mat3)
 mat_impl!(Mat3, 3)
 one_impl!(Mat3, [ _1 | _0 | _0 |
                   _0 | _1 | _0 |
@@ -94,6 +97,7 @@ column_impl!(Mat3, 3)
 pub struct Mat4<N>
 { mij: [N, ..4 * 4] }
 
+clone_impl!(Mat4)
 mat_impl!(Mat4, 4)
 one_impl!(Mat4, [
           _1 | _0 | _0 | _0 |
@@ -130,6 +134,7 @@ column_impl!(Mat4, 4)
 pub struct Mat5<N>
 { mij: [N, ..5 * 5] }
 
+clone_impl!(Mat5)
 mat_impl!(Mat5, 5)
 one_impl!(Mat5, [
           _1 | _0 | _0 | _0 | _0 |
@@ -169,6 +174,7 @@ column_impl!(Mat5, 5)
 pub struct Mat6<N>
 { mij: [N, ..6 * 6] }
 
+clone_impl!(Mat6)
 mat_impl!(Mat6, 6)
 one_impl!(Mat6, [
           _1 | _0 | _0 | _0 | _0 | _0 |
diff --git a/src/mat_impl.rs b/src/mat_impl.rs
index 0b7ed0d6..6918f2cb 100644
--- a/src/mat_impl.rs
+++ b/src/mat_impl.rs
@@ -1,5 +1,22 @@
 #[macro_escape];
 
+macro_rules! clone_impl(
+   // FIXME: use 'Clone' alone. For the moment, we need 'Copy' because the automatic
+   // implementation of Clone for [t, ..n] is badly typed.
+  ($t: ident) => (
+    impl<N: Clone + Copy> Clone for $t<N>
+    {
+      #[inline]
+      fn clone(&self) -> $t<N>
+      {
+        $t {
+          mij: copy self.mij
+        }
+      }
+    }
+  )
+)
+
 macro_rules! mat_impl(
   ($t: ident, $dim: expr) => (
     impl<N> $t<N>
@@ -17,13 +34,13 @@ macro_rules! mat_impl(
 
 macro_rules! one_impl(
   ($t: ident, [ $($value: ident)|+ ] ) => (
-    impl<N: Copy + One + Zero> One for $t<N>
+    impl<N: Clone + One + Zero> One for $t<N>
     {
       #[inline]
       fn one() -> $t<N>
       {
         let (_0, _1) = (Zero::zero::<N>(), One::one::<N>());
-        return $t::new( [ $( copy $value, )+ ] )
+        return $t::new( [ $( $value.clone(), )+ ] )
       }
     }
   )
@@ -31,13 +48,13 @@ macro_rules! one_impl(
 
 macro_rules! zero_impl(
   ($t: ident, [ $($value: ident)|+ ] ) => (
-    impl<N: Copy + Zero> Zero for $t<N>
+    impl<N: Clone + Zero> Zero for $t<N>
     {
       #[inline]
       fn zero() -> $t<N>
       {
-        let _0 = Zero::zero();
-        return $t::new( [ $( copy $value, )+ ] )
+        let _0 = Zero::zero::<N>();
+        return $t::new( [ $( $value.clone(), )+ ] )
       }
 
      #[inline]
@@ -60,11 +77,11 @@ macro_rules! dim_impl(
 
 macro_rules! mat_indexable_impl(
   ($t: ident, $dim: expr) => (
-    impl<N: Copy> Indexable<(uint, uint), N> for $t<N>
+    impl<N: Clone> Indexable<(uint, uint), N> for $t<N>
     {
       #[inline]
       pub fn at(&self, (i, j): (uint, uint)) -> N
-      { copy self.mij[self.offset(i, j)] }
+      { self.mij[self.offset(i, j)].clone() }
 
       #[inline]
       pub fn set(&mut self, (i, j): (uint, uint), t: N)
@@ -75,7 +92,7 @@ macro_rules! mat_indexable_impl(
 
 macro_rules! column_impl(
   ($t: ident, $dim: expr) => (
-    impl<N: Copy, V: Zero + Iterable<N> + IterableMut<N>> Column<V> for $t<N>
+    impl<N: Clone, V: Zero + Iterable<N> + IterableMut<N>> Column<V> for $t<N>
     {
       fn set_column(&mut self, col: uint, v: V)
       {
@@ -84,7 +101,7 @@ macro_rules! column_impl(
           if i == Dim::dim::<$t<N>>()
           { break }
 
-          self.set((i, col), copy *e);
+          self.set((i, col), e.clone());
         }
       }
 
@@ -108,7 +125,7 @@ macro_rules! column_impl(
 
 macro_rules! mul_impl(
   ($t: ident, $dim: expr) => (
-    impl<N: Copy + Ring>
+    impl<N: Clone + Ring>
     Mul<$t<N>, $t<N>> for $t<N>
     {
       fn mul(&self, other: &$t<N>) -> $t<N>
@@ -136,7 +153,7 @@ macro_rules! mul_impl(
 
 macro_rules! rmul_impl(
   ($t: ident, $v: ident, $dim: expr) => (
-    impl<N: Copy + Ring>
+    impl<N: Clone + Ring>
     RMul<$v<N>> for $t<N>
     {
       fn rmul(&self, other: &$v<N>) -> $v<N>
@@ -157,7 +174,7 @@ macro_rules! rmul_impl(
 
 macro_rules! lmul_impl(
   ($t: ident, $v: ident, $dim: expr) => (
-    impl<N: Copy + Ring>
+    impl<N: Clone + Ring>
     LMul<$v<N>> for $t<N>
     {
       fn lmul(&self, other: &$v<N>) -> $v<N>
@@ -179,7 +196,7 @@ macro_rules! lmul_impl(
 
 macro_rules! transform_impl(
   ($t: ident, $v: ident) => (
-    impl<N: Copy + DivisionRing + Eq>
+    impl<N: Clone + Copy + DivisionRing + Eq>
     Transform<$v<N>> for $t<N>
     {
       #[inline]
@@ -188,27 +205,34 @@ macro_rules! transform_impl(
     
       #[inline]
       fn inv_transform(&self, v: &$v<N>) -> $v<N>
-      { self.inverse().transform_vec(v) }
+      {
+        match self.inverse()
+        {
+          Some(t) => t.transform_vec(v),
+          None    => fail!("Cannot use inv_transform on a non-inversible matrix.")
+        }
+      }
     }
   )
 )
 
 macro_rules! inv_impl(
   ($t: ident, $dim: expr) => (
-    impl<N: Copy + Eq + DivisionRing>
+    impl<N: Clone + Copy + Eq + DivisionRing>
     Inv for $t<N>
     {
       #[inline]
-      fn inverse(&self) -> $t<N>
+      fn inverse(&self) -> Option<$t<N>>
       {
-        let mut res : $t<N> = copy *self;
+        let mut res : $t<N> = self.clone();
     
-        res.invert();
-    
-        res
+        if res.invert()
+        { Some(res) }
+        else
+        { None }
       }
     
-      fn invert(&mut self)
+      fn invert(&mut self) -> bool
       {
         let mut res: $t<N> = One::one();
         let     _0N: N     = Zero::zero();
@@ -229,6 +253,9 @@ macro_rules! inv_impl(
     
             n0 = n0 + 1;
           }
+
+          if n0 == $dim
+          { return false }
     
           // swap pivot line
           if n0 != k
@@ -279,6 +306,8 @@ macro_rules! inv_impl(
         }
     
         *self = res;
+
+        true
       }
     }
   )
@@ -286,12 +315,12 @@ macro_rules! inv_impl(
 
 macro_rules! transpose_impl(
   ($t: ident, $dim: expr) => (
-    impl<N: Copy> Transpose for $t<N>
+    impl<N: Clone + Copy> Transpose for $t<N>
     {
       #[inline]
       fn transposed(&self) -> $t<N>
       {
-        let mut res = copy *self;
+        let mut res = self.clone();
     
         res.transpose();
     
@@ -355,7 +384,7 @@ macro_rules! rand_impl(
 
 macro_rules! to_homogeneous_impl(
   ($t: ident, $t2: ident, $dim: expr) => (
-    impl<N: One + Zero + Copy> ToHomogeneous<$t2<N>> for $t<N>
+    impl<N: One + Zero + Clone> ToHomogeneous<$t2<N>> for $t<N>
     {
       fn to_homogeneous(&self) -> $t2<N>
       {
@@ -375,7 +404,7 @@ macro_rules! to_homogeneous_impl(
 
 macro_rules! from_homogeneous_impl(
   ($t: ident, $t2: ident, $dim2: expr) => (
-    impl<N: One + Zero + Copy> FromHomogeneous<$t2<N>> for $t<N>
+    impl<N: One + Zero + Clone> FromHomogeneous<$t2<N>> for $t<N>
     {
       fn from_homogeneous(m: &$t2<N>) -> $t<N>
       {
diff --git a/src/mat_spec.rs b/src/mat_spec.rs
index 3f2613c0..6f85f306 100644
--- a/src/mat_spec.rs
+++ b/src/mat_spec.rs
@@ -8,21 +8,26 @@ impl<N: Copy + DivisionRing>
 Inv for Mat1<N>
 {
   #[inline]
-  fn inverse(&self) -> Mat1<N>
+  fn inverse(&self) -> Option<Mat1<N>>
   {
     let mut res : Mat1<N> = copy *self;
 
-    res.invert();
-
-    res
+    if res.invert()
+    { Some(res) }
+    else
+    { None }
   }
 
   #[inline]
-  fn invert(&mut self)
+  fn invert(&mut self) -> bool
   {
-    assert!(!self.mij[0].is_zero());
-
-    self.mij[0] = One::one::<N>() / self.mij[0]
+    if self.mij[0].is_zero()
+    { false }
+    else
+    {
+      self.mij[0] = One::one::<N>() / self.mij[0];
+      true
+    }
   }
 }
 
@@ -30,24 +35,30 @@ impl<N: Copy + DivisionRing>
 Inv for Mat2<N>
 {
   #[inline]
-  fn inverse(&self) -> Mat2<N>
+  fn inverse(&self) -> Option<Mat2<N>>
   {
     let mut res : Mat2<N> = copy *self;
 
-    res.invert();
-
-    res
+    if res.invert()
+    { Some(res) }
+    else
+    { None }
   }
 
   #[inline]
-  fn invert(&mut self)
+  fn invert(&mut self) -> bool
   {
     let det = self.mij[0 * 2 + 0] * self.mij[1 * 2 + 1] - self.mij[1 * 2 + 0] * self.mij[0 * 2 + 1];
 
-    assert!(!det.is_zero());
+    if det.is_zero()
+    { false }
+    else
+    {
+      *self = Mat2::new([self.mij[1 * 2 + 1] / det , -self.mij[0 * 2 + 1] / det,
+                         -self.mij[1 * 2 + 0] / det, self.mij[0 * 2 + 0] / det]);
 
-    *self = Mat2::new([self.mij[1 * 2 + 1] / det , -self.mij[0 * 2 + 1] / det,
-                           -self.mij[1 * 2 + 0] / det, self.mij[0 * 2 + 0] / det])
+      true
+    }
   }
 }
 
@@ -55,17 +66,18 @@ impl<N: Copy + DivisionRing>
 Inv for Mat3<N>
 {
   #[inline]
-  fn inverse(&self) -> Mat3<N>
+  fn inverse(&self) -> Option<Mat3<N>>
   {
     let mut res = copy *self;
 
-    res.invert();
-
-    res
+    if res.invert()
+    { Some(res) }
+    else
+    { None }
   }
 
   #[inline]
-  fn invert(&mut self)
+  fn invert(&mut self) -> bool
   {
     let minor_m12_m23 = self.mij[1 * 3 + 1] * self.mij[2 * 3 + 2] - self.mij[2 * 3 + 1] * self.mij[1 * 3 + 2];
     let minor_m11_m23 = self.mij[1 * 3 + 0] * self.mij[2 * 3 + 2] - self.mij[2 * 3 + 0] * self.mij[1 * 3 + 2];
@@ -75,20 +87,25 @@ Inv for Mat3<N>
               - self.mij[0 * 3 + 1] * minor_m11_m23
               + self.mij[0 * 3 + 2] * minor_m11_m22;
 
-    assert!(!det.is_zero());
+    if det.is_zero()
+    { false }
+    else
+    {
+      *self = Mat3::new( [
+        (minor_m12_m23  / det),
+        ((self.mij[0 * 3 + 2] * self.mij[2 * 3 + 1] - self.mij[2 * 3 + 2] * self.mij[0 * 3 + 1]) / det),
+        ((self.mij[0 * 3 + 1] * self.mij[1 * 3 + 2] - self.mij[1 * 3 + 1] * self.mij[0 * 3 + 2]) / det),
 
-    *self = Mat3::new( [
-      (minor_m12_m23  / det),
-      ((self.mij[0 * 3 + 2] * self.mij[2 * 3 + 1] - self.mij[2 * 3 + 2] * self.mij[0 * 3 + 1]) / det),
-      ((self.mij[0 * 3 + 1] * self.mij[1 * 3 + 2] - self.mij[1 * 3 + 1] * self.mij[0 * 3 + 2]) / det),
+        (-minor_m11_m23 / det),
+        ((self.mij[0 * 3 + 0] * self.mij[2 * 3 + 2] - self.mij[2 * 3 + 0] * self.mij[0 * 3 + 2]) / det),
+        ((self.mij[0 * 3 + 2] * self.mij[1 * 3 + 0] - self.mij[1 * 3 + 2] * self.mij[0 * 3 + 0]) / det),
 
-      (-minor_m11_m23 / det),
-      ((self.mij[0 * 3 + 0] * self.mij[2 * 3 + 2] - self.mij[2 * 3 + 0] * self.mij[0 * 3 + 2]) / det),
-      ((self.mij[0 * 3 + 2] * self.mij[1 * 3 + 0] - self.mij[1 * 3 + 2] * self.mij[0 * 3 + 0]) / det),
+        (minor_m11_m22  / det),
+        ((self.mij[0 * 3 + 1] * self.mij[2 * 3 + 0] - self.mij[2 * 3 + 1] * self.mij[0 * 3 + 0]) / det),
+        ((self.mij[0 * 3 + 0] * self.mij[1 * 3 + 1] - self.mij[1 * 3 + 0] * self.mij[0 * 3 + 1]) / det)
+      ] );
 
-      (minor_m11_m22  / det),
-      ((self.mij[0 * 3 + 1] * self.mij[2 * 3 + 0] - self.mij[2 * 3 + 1] * self.mij[0 * 3 + 0]) / det),
-      ((self.mij[0 * 3 + 0] * self.mij[1 * 3 + 1] - self.mij[1 * 3 + 0] * self.mij[0 * 3 + 1]) / det)
-    ] )
+      true
+    }
   }
 }
diff --git a/src/nalgebra.rc b/src/nalgebra.rc
index bd3e6129..078ee818 100644
--- a/src/nalgebra.rc
+++ b/src/nalgebra.rc
@@ -34,6 +34,7 @@ pub mod adaptors
 /// Useful linear-algebra related traits.
 pub mod traits
 {
+  pub mod sample;
   pub mod indexable;
   pub mod column;
   pub mod iterable;
diff --git a/src/tests/mat.rs b/src/tests/mat.rs
index d7ed2ea0..f7bff18d 100644
--- a/src/tests/mat.rs
+++ b/src/tests/mat.rs
@@ -25,7 +25,7 @@ macro_rules! test_inv_mat_impl(
     {
       let randmat : $t = random();
 
-      assert!((randmat.inverse() * randmat).approx_eq(&One::one()));
+      assert!((randmat.inverse().unwrap() * randmat).approx_eq(&One::one()));
     }
   );
 )
diff --git a/src/traits/inv.rs b/src/traits/inv.rs
index fc42bebe..932b2a1c 100644
--- a/src/traits/inv.rs
+++ b/src/traits/inv.rs
@@ -4,7 +4,7 @@
 pub trait Inv
 {
   /// Returns the inverse of an element.
-  fn inverse(&self) -> Self;
+  fn inverse(&self) -> Option<Self>;
   /// Inplace version of `inverse`.
-  fn invert(&mut self);
+  fn invert(&mut self) -> bool;
 }
diff --git a/src/traits/sample.rs b/src/traits/sample.rs
new file mode 100644
index 00000000..a0ee726d
--- /dev/null
+++ b/src/traits/sample.rs
@@ -0,0 +1,4 @@
+pub trait UniformSphereSample
+{
+  pub fn sample(&fn(&'static Self));
+}
diff --git a/src/vec.rs b/src/vec.rs
index 26881efb..3bb6d9ed 100644
--- a/src/vec.rs
+++ b/src/vec.rs
@@ -24,6 +24,7 @@ mod vec_impl;
 pub struct Vec1<N>
 { at: [N, ..1] }
 
+clone_impl!(Vec1)
 new_impl!(Vec1, 1)
 new_repeat_impl!(Vec1, elem, [elem])
 indexable_impl!(Vec1)
@@ -58,6 +59,7 @@ from_homogeneous_impl!(Vec2, Vec1, 2)
 pub struct Vec2<N>
 { at: [N, ..2] }
 
+clone_impl!(Vec2)
 new_impl!(Vec2, 2)
 new_repeat_impl!(Vec2, elem, [elem | elem])
 indexable_impl!(Vec2)
@@ -92,6 +94,7 @@ from_homogeneous_impl!(Vec3, Vec2, 3)
 pub struct Vec3<N>
 { at: [N, ..3] }
 
+clone_impl!(Vec3)
 new_impl!(Vec3, 3)
 new_repeat_impl!(Vec3, elem, [elem | elem | elem])
 indexable_impl!(Vec3)
@@ -126,6 +129,7 @@ from_homogeneous_impl!(Vec4, Vec3, 4)
 pub struct Vec4<N>
 { at: [N, ..4] }
 
+clone_impl!(Vec4)
 new_impl!(Vec4, 4)
 new_repeat_impl!(Vec4, elem, [elem | elem | elem | elem])
 indexable_impl!(Vec4)
@@ -160,6 +164,7 @@ from_homogeneous_impl!(Vec5, Vec4, 5)
 pub struct Vec5<N>
 { at: [N, ..5] }
 
+clone_impl!(Vec5)
 new_impl!(Vec5, 5)
 new_repeat_impl!(Vec5, elem, [elem | elem | elem | elem | elem])
 indexable_impl!(Vec5)
@@ -194,6 +199,7 @@ from_homogeneous_impl!(Vec6, Vec5, 6)
 pub struct Vec6<N>
 { at: [N, ..6] }
 
+clone_impl!(Vec6)
 new_impl!(Vec6, 6)
 new_repeat_impl!(Vec6, elem, [elem | elem | elem | elem | elem | elem])
 indexable_impl!(Vec6)
diff --git a/src/vec_impl.rs b/src/vec_impl.rs
index 63716426..a2e99e7d 100644
--- a/src/vec_impl.rs
+++ b/src/vec_impl.rs
@@ -1,5 +1,19 @@
 #[macro_escape];
 
+macro_rules! clone_impl(
+  ($t:ident) => (
+    // FIXME: use 'Clone' alone. For the moment, we need 'Copy' because the automatic
+    // implementation of Clone for [t, ..n] is badly typed.
+    impl<N: Clone + Copy> Clone for $t<N>
+    {
+      fn clone(&self) -> $t<N>
+      {
+        $t { at: copy self.at }
+      }
+    }
+  )
+)
+
 macro_rules! new_impl(
   ($t: ident, $dim: expr) => (
     impl<N> $t<N>
@@ -13,11 +27,11 @@ macro_rules! new_impl(
 
 macro_rules! indexable_impl(
   ($t: ident) => (
-    impl<N: Copy> Indexable<uint, N> for $t<N>
+    impl<N: Clone> Indexable<uint, N> for $t<N>
     {
       #[inline]
       pub fn at(&self, i: uint) -> N
-      { copy self.at[i] }
+      { self.at[i].clone() }
 
       #[inline]
       pub fn set(&mut self, i: uint, val: N)
@@ -28,11 +42,11 @@ macro_rules! indexable_impl(
 
 macro_rules! new_repeat_impl(
   ($t: ident, $param: ident, [ $($elem: ident)|+ ]) => (
-    impl<N: Copy> $t<N>
+    impl<N: Clone> $t<N>
     {
       #[inline]
       pub fn new_repeat($param: N) -> $t<N>
-      { $t{ at: [ $( copy $elem, )+ ] } }
+      { $t{ at: [ $( $elem.clone(), )+ ] } }
     }
   )
 )
@@ -86,7 +100,7 @@ macro_rules! dim_impl(
 // FIXME: add the possibility to specialize that
 macro_rules! basis_impl(
   ($t: ident, $dim: expr) => (
-    impl<N: Copy + DivisionRing + Algebraic + ApproxEq<N>> Basis for $t<N>
+    impl<N: Clone + Copy + DivisionRing + Algebraic + ApproxEq<N>> Basis for $t<N>
     {
       pub fn canonical_basis(f: &fn($t<N>))
       {
@@ -115,7 +129,7 @@ macro_rules! basis_impl(
           if basis.len() == $dim - 1
           { break; }
     
-          let mut elt = copy basis_element;
+          let mut elt = basis_element.clone();
     
           elt = elt - self.scalar_mul(&basis_element.dot(self));
     
@@ -126,7 +140,7 @@ macro_rules! basis_impl(
           {
             let new_element = elt.normalized();
 
-            f(copy new_element);
+            f(new_element.clone());
 
             basis.push(new_element);
           }
@@ -138,7 +152,7 @@ macro_rules! basis_impl(
 
 macro_rules! add_impl(
   ($t: ident) => (
-    impl<N: Copy + Add<N,N>> Add<$t<N>, $t<N>> for $t<N>
+    impl<N: Clone + Add<N,N>> Add<$t<N>, $t<N>> for $t<N>
     {
       #[inline]
       fn add(&self, other: &$t<N>) -> $t<N>
@@ -154,7 +168,7 @@ macro_rules! add_impl(
 
 macro_rules! sub_impl(
   ($t: ident) => (
-    impl<N: Copy + Sub<N,N>> Sub<$t<N>, $t<N>> for $t<N>
+    impl<N: Clone + Sub<N,N>> Sub<$t<N>, $t<N>> for $t<N>
     {
       #[inline]
       fn sub(&self, other: &$t<N>) -> $t<N>
@@ -290,11 +304,11 @@ macro_rules! scalar_sub_impl(
 
 macro_rules! translation_impl(
   ($t: ident) => (
-    impl<N: Copy + Add<N, N> + Neg<N>> Translation<$t<N>> for $t<N>
+    impl<N: Clone + Copy + Add<N, N> + Neg<N>> Translation<$t<N>> for $t<N>
     {
       #[inline]
       fn translation(&self) -> $t<N>
-      { copy *self }
+      { self.clone() }
 
       #[inline]
       fn inv_translation(&self) -> $t<N>
@@ -309,7 +323,7 @@ macro_rules! translation_impl(
 
 macro_rules! translatable_impl(
   ($t: ident) => (
-    impl<N: Add<N, N> + Neg<N> + Copy> Translatable<$t<N>, $t<N>> for $t<N>
+    impl<N: Add<N, N> + Neg<N> + Clone> Translatable<$t<N>, $t<N>> for $t<N>
     {
       #[inline]
       fn translated(&self, t: &$t<N>) -> $t<N>
@@ -320,7 +334,7 @@ macro_rules! translatable_impl(
 
 macro_rules! norm_impl(
   ($t: ident, $dim: expr) => (
-    impl<N: Copy + DivisionRing + Algebraic> Norm<N> for $t<N>
+    impl<N: Clone + Copy + DivisionRing + Algebraic> Norm<N> for $t<N>
     {
       #[inline]
       fn sqnorm(&self) -> N
@@ -333,7 +347,7 @@ macro_rules! norm_impl(
       #[inline]
       fn normalized(&self) -> $t<N>
       {
-        let mut res : $t<N> = copy *self;
+        let mut res : $t<N> = self.clone();
     
         res.normalize();
     
@@ -383,7 +397,7 @@ macro_rules! approx_eq_impl(
 
 macro_rules! zero_impl(
   ($t: ident) => (
-    impl<N: Copy + Zero> Zero for $t<N>
+    impl<N: Clone + Zero> Zero for $t<N>
     {
       #[inline]
       fn zero() -> $t<N>
@@ -398,7 +412,7 @@ macro_rules! zero_impl(
 
 macro_rules! one_impl(
   ($t: ident) => (
-    impl<N: Copy + One> One for $t<N>
+    impl<N: Clone + One> One for $t<N>
     {
       #[inline]
       fn one() -> $t<N>
@@ -420,13 +434,13 @@ macro_rules! rand_impl(
 
 macro_rules! from_any_iterator_impl(
   ($t: ident, $param: ident, [ $($elem: ident)|+ ]) => (
-    impl<N: Copy> FromAnyIterator<N> for $t<N>
+    impl<N: Clone> FromAnyIterator<N> for $t<N>
     {
       fn from_iterator<'l>($param: &mut VecIterator<'l, N>) -> $t<N>
-      { $t { at: [ $( copy *$elem.next().unwrap(), )+ ] } }
+      { $t { at: [ $( $elem.next().unwrap().clone(), )+ ] } }
 
       fn from_mut_iterator<'l>($param: &mut VecMutIterator<'l, N>) -> $t<N>
-      { $t { at: [ $( copy *$elem.next().unwrap(), )+ ] } }
+      { $t { at: [ $( $elem.next().unwrap().clone(), )+ ] } }
     }
   )
 )
@@ -443,7 +457,7 @@ macro_rules! from_iterator_impl(
 
 macro_rules! bounded_impl(
   ($t: ident) => (
-    impl<N: Bounded + Copy> Bounded for $t<N>
+    impl<N: Bounded + Clone> Bounded for $t<N>
     {
       #[inline]
       fn max_value() -> $t<N>
@@ -459,14 +473,14 @@ macro_rules! bounded_impl(
 macro_rules! to_homogeneous_impl(
   ($t: ident, $t2: ident) =>
   {
-    impl<N: Copy + One> ToHomogeneous<$t2<N>> for $t<N>
+    impl<N: Clone + One> ToHomogeneous<$t2<N>> for $t<N>
     {
       fn to_homogeneous(&self) -> $t2<N>
       {
         let mut res: $t2<N> = One::one();
 
         for self.iter().zip(res.mut_iter()).advance |(in, out)|
-        { *out = copy *in }
+        { *out = in.clone() }
 
         res
       }
@@ -477,14 +491,14 @@ macro_rules! to_homogeneous_impl(
 macro_rules! from_homogeneous_impl(
   ($t: ident, $t2: ident, $dim2: expr) =>
   {
-    impl<N: Copy + Div<N, N> + One + Zero> FromHomogeneous<$t2<N>> for $t<N>
+    impl<N: Clone + Div<N, N> + One + Zero> FromHomogeneous<$t2<N>> for $t<N>
     {
       fn from_homogeneous(v: &$t2<N>) -> $t<N>
       {
         let mut res: $t<N> = Zero::zero();
 
         for v.iter().zip(res.mut_iter()).advance |(in, out)|
-        { *out = copy *in }
+        { *out = in.clone() }
 
         res.scalar_div(&v.at[$dim2 - 1]);
 
diff --git a/src/vec_spec.rs b/src/vec_spec.rs
index 164b5e4d..dabcc548 100644
--- a/src/vec_spec.rs
+++ b/src/vec_spec.rs
@@ -3,6 +3,7 @@ use traits::basis::Basis;
 use traits::cross::Cross;
 use traits::division_ring::DivisionRing;
 use traits::norm::Norm;
+use traits::sample::UniformSphereSample;
 use vec::{Vec1, Vec2, Vec3};
 
 impl<N: Mul<N, N> + Sub<N, N>> Cross<Vec1<N>> for Vec2<N>
@@ -36,7 +37,7 @@ impl<N: One> Basis for Vec1<N>
   { }
 }
 
-impl<N: Copy + One + Zero + Neg<N>> Basis for Vec2<N>
+impl<N: Clone + One + Zero + Neg<N>> Basis for Vec2<N>
 {
   #[inline]
   fn canonical_basis(f: &fn(Vec2<N>))
@@ -47,10 +48,10 @@ impl<N: Copy + One + Zero + Neg<N>> Basis for Vec2<N>
 
   #[inline]
   fn orthonormal_subspace_basis(&self, f: &fn(Vec2<N>))
-  { f(Vec2::new([-self.at[1], copy self.at[0]])) }
+  { f(Vec2::new([-self.at[1], self.at[0].clone()])) }
 }
 
-impl<N: Copy + DivisionRing + Ord + Algebraic>
+impl<N: Clone + Copy + DivisionRing + Ord + Algebraic>
 Basis for Vec3<N>
 {
   #[inline(always)]
@@ -65,12 +66,46 @@ Basis for Vec3<N>
   fn orthonormal_subspace_basis(&self, f: &fn(Vec3<N>))
   {
       let a = 
-        if abs(copy self.at[0]) > abs(copy self.at[1])
-        { Vec3::new([copy self.at[2], Zero::zero(), -copy self.at[0]]).normalized() }
+        if abs(self.at[0].clone()) > abs(self.at[1].clone())
+        { Vec3::new([self.at[2].clone(), Zero::zero(), -self.at[0]]).normalized() }
         else
-        { Vec3::new([Zero::zero(), -self.at[2], copy self.at[1]]).normalized() };
+        { Vec3::new([Zero::zero(), -self.at[2], self.at[1].clone()]).normalized() };
 
       f(a.cross(self));
       f(a);
   }
 }
+
+// FIXME: this bad: this fixes definitly the number of samples…
+static SAMPLES_2_F64: [Vec2<f64>, ..21] = [
+  Vec2 { at: [1.0, 0.0] },
+  Vec2 { at: [0.95557281, 0.29475517] },
+  Vec2 { at: [0.82623877, 0.56332006] },
+  Vec2 { at: [0.6234898, 0.78183148] },
+  Vec2 { at: [0.36534102, 0.93087375] },
+  Vec2 { at: [0.07473009, 0.9972038] },
+  Vec2 { at: [-0.22252093, 0.97492791] },
+  Vec2 { at: [-0.5, 0.8660254] },
+  Vec2 { at: [-0.73305187, 0.68017274] },
+  Vec2 { at: [-0.90096887, 0.43388374] },
+  Vec2 { at: [-0.98883083, 0.14904227] },
+  Vec2 { at: [-0.98883083, -0.14904227] },
+  Vec2 { at: [-0.90096887, -0.43388374] },
+  Vec2 { at: [-0.73305187, -0.68017274] },
+  Vec2 { at: [-0.5, -0.8660254] },
+  Vec2 { at: [-0.22252093, -0.97492791] },
+  Vec2 { at: [0.07473009, -0.9972038] },
+  Vec2 { at: [0.36534102, -0.93087375] },
+  Vec2 { at: [0.6234898, -0.78183148] },
+  Vec2 { at: [0.82623877, -0.56332006] },
+  Vec2 { at: [0.95557281, -0.29475517] },
+];
+
+impl UniformSphereSample for Vec2<f64>
+{
+  pub fn sample(f: &fn(&'static Vec2<f64>))
+  {
+    for SAMPLES_2_F64.iter().advance |sample|
+    { f(sample) }
+  }
+}