diff --git a/stubs/Col.php b/stubs/Col.php
index bb6772a..c579a49 100644
--- a/stubs/Col.php
+++ b/stubs/Col.php
@@ -7,7 +7,7 @@ namespace Arma;
  *
  * @package Arma
  */
-interface Col extends Internal\Dense, Internal\Vector
+interface Col extends Internal\DenseVector
 {
 
 }
diff --git a/stubs/Mat.php b/stubs/Mat.php
index 130a3a5..a268b13 100644
--- a/stubs/Mat.php
+++ b/stubs/Mat.php
@@ -12,8 +12,8 @@ interface Mat extends Internal\Dense, Internal\Matrix
     /**
      * Construct the matrix to have user specified dimensions and fill with specified pattern.
      *
-     * @param int $n_rows
-     * @param int $n_cols
+     * @param int $n_rows[optional]
+     * @param int $n_cols[optional]
      * @param int $fill[optional]
      * @return static
      */
diff --git a/stubs/Row.php b/stubs/Row.php
index c5961b3..22077fe 100644
--- a/stubs/Row.php
+++ b/stubs/Row.php
@@ -7,7 +7,7 @@ namespace Arma;
  *
  * @package Arma
  */
-interface Row extends Internal\Dense, Internal\Vector
+interface Row extends Internal\DenseVector
 {
 
 }
diff --git a/stubs/SpCol.php b/stubs/SpCol.php
new file mode 100644
index 0000000..334834e
--- /dev/null
+++ b/stubs/SpCol.php
@@ -0,0 +1,8 @@
+<?php
+
+namespace Arma;
+
+interface SpCol extends Internal\Sparse, Internal\Vector, Internal\ResizableVector
+{
+
+}
diff --git a/stubs/SpRow.php b/stubs/SpRow.php
new file mode 100644
index 0000000..b397b0b
--- /dev/null
+++ b/stubs/SpRow.php
@@ -0,0 +1,8 @@
+<?php
+
+namespace Arma;
+
+interface SpRow extends Internal\Sparse, Internal\Vector, Internal\ResizableVector
+{
+
+}
diff --git a/stubs/impl/SpCxDCol.php b/stubs/impl/SpCxDCol.php
new file mode 100644
index 0000000..f494cb9
--- /dev/null
+++ b/stubs/impl/SpCxDCol.php
@@ -0,0 +1,8 @@
+<?php
+
+namespace Arma;
+
+class SpCxDCol implements SpCol
+{
+
+}
diff --git a/stubs/impl/SpCxDRow.php b/stubs/impl/SpCxDRow.php
new file mode 100644
index 0000000..5fbd605
--- /dev/null
+++ b/stubs/impl/SpCxDRow.php
@@ -0,0 +1,8 @@
+<?php
+
+namespace Arma;
+
+class SpCxDRow implements SpRow
+{
+
+}
diff --git a/stubs/impl/SpDCol.php b/stubs/impl/SpDCol.php
new file mode 100644
index 0000000..7b67cc6
--- /dev/null
+++ b/stubs/impl/SpDCol.php
@@ -0,0 +1,8 @@
+<?php
+
+namespace Arma;
+
+class SpDCol implements SpCol
+{
+
+}
diff --git a/stubs/impl/SpDRow.php b/stubs/impl/SpDRow.php
new file mode 100644
index 0000000..8930a98
--- /dev/null
+++ b/stubs/impl/SpDRow.php
@@ -0,0 +1,8 @@
+<?php
+
+namespace Arma;
+
+class SpDRow implements SpRow
+{
+
+}
diff --git a/stubs/impl/SpICol.php b/stubs/impl/SpICol.php
new file mode 100644
index 0000000..d9b7d37
--- /dev/null
+++ b/stubs/impl/SpICol.php
@@ -0,0 +1,8 @@
+<?php
+
+namespace Arma;
+
+class SpICol implements SpCol
+{
+
+}
diff --git a/stubs/impl/SpIRow.php b/stubs/impl/SpIRow.php
new file mode 100644
index 0000000..2c3cbec
--- /dev/null
+++ b/stubs/impl/SpIRow.php
@@ -0,0 +1,8 @@
+<?php
+
+namespace Arma;
+
+class SpIRow implements SpRow
+{
+
+}
diff --git a/stubs/internal/DenseVector.php b/stubs/internal/DenseVector.php
new file mode 100644
index 0000000..ce0254f
--- /dev/null
+++ b/stubs/internal/DenseVector.php
@@ -0,0 +1,36 @@
+<?php
+
+namespace Arma\Internal;
+
+interface DenseVector extends Dense, Vector
+{
+    // Initialization
+
+    /**
+     * Set all the elements of an object to one, optionally first changing the size to specified dimensions.
+     *
+     * @param int $n_elem[optional]
+     * @return void
+     */
+    function ones($n_elem);
+
+    /**
+     * Set all the elements to random values, optionally first changing the size to specified dimensions.
+     *
+     * Uses a uniform distribution in the [0,1] interval.
+     *
+     * @param int $n_elem[optional]
+     * @return void
+     */
+    function randu($n_elem);
+
+    /**
+     * Set all the elements to random values, optionally first changing the size to specified dimensions.
+     *
+     * Uses a normal/Gaussian distribution with zero mean and unit variance.
+     *
+     * @param int $n_elem[optional]
+     * @return void
+     */
+    function randn($n_elem);
+}
diff --git a/stubs/internal/Matrix.php b/stubs/internal/Matrix.php
index e94be3f..c4f3c78 100644
--- a/stubs/internal/Matrix.php
+++ b/stubs/internal/Matrix.php
@@ -12,8 +12,8 @@ interface Matrix
     /**
      * Set the elements of an object to zero, optionally first changing the size to specified dimensions.
      *
-     * @param $n_rows[optional]
-     * @param $n_cols[optional]
+     * @param int $n_rows[optional]
+     * @param int $n_cols[optional]
      * @return void
      */
     function zeros($n_rows, $n_cols);
@@ -22,8 +22,8 @@ interface Matrix
      * Set the elements along the main diagonal to one and off-diagonal elements to zero, optionally
      * first changing the size to specified dimensions.
      *
-     * @param $n_rows[optional]
-     * @param $n_cols[optional]
+     * @param int $n_rows[optional]
+     * @param int $n_cols[optional]
      * @return void
      */
     function eye($n_rows, $n_cols);
diff --git a/stubs/internal/Vector.php b/stubs/internal/Vector.php
index 26b81b0..f0225c2 100644
--- a/stubs/internal/Vector.php
+++ b/stubs/internal/Vector.php
@@ -3,16 +3,18 @@
 namespace Arma\Internal;
 
 /**
- * Interface for vectors (Col and Row).
+ * Interface for vectors (Col, Row, SpCol and SpRow).
  *
  * @package Arma\Internal
  */
 interface Vector
 {
+    // Constructors
+
     /**
      * Construct the vector to have user specified size and fill with specified pattern.
      *
-     * @param int $n_elem
+     * @param int $n_elem[optional]
      * @param int $fill[optional]
      * @return static
      */
@@ -28,42 +30,16 @@ interface Vector
      */
     static function fromString($text);
 
+    // Initialization
+
     /**
      * Set the elements of an object to zero, optionally first changing the size to specified dimensions.
      *
-     * @param $n_elem[optional]
+     * @param int $n_elem[optional]
      * @return void
      */
     function zeros($n_elem);
 
-    /**
-     * Set all the elements of an object to one, optionally first changing the size to specified dimensions.
-     *
-     * @param $n_elem[optional]
-     * @return void
-     */
-    function ones($n_elem);
-
-    /**
-     * Set all the elements to random values, optionally first changing the size to specified dimensions.
-     *
-     * Uses a uniform distribution in the [0,1] interval.
-     *
-     * @param $n_elem[optional]
-     * @return void
-     */
-    function randu($n_elem);
-
-    /**
-     * Set all the elements to random values, optionally first changing the size to specified dimensions.
-     *
-     * Uses a normal/Gaussian distribution with zero mean and unit variance.
-     *
-     * @param $n_elem[optional]
-     * @return void
-     */
-    function randn($n_elem);
-
     // Vector subview
 
     /**