Small improvements.

LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) [2016] [Wiebe-Marten Wijnja]
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

lib/matrix.ex

@@ -3,8 +3,9 @@ defmodule Matrix do
     @doc false
     def inspect(matrix, _opts) do
       """
-      #Matrix-(#{Tensor.Inspect.dimension_string(matrix)})
+      #Matrix<(#{Tensor.Inspect.dimension_string(matrix)})
       #{inspect_contents(matrix)}
+      >
       """
     end
 
@@ -306,8 +307,36 @@ defmodule Matrix do
 
 
   def product(_a = %Tensor{dimensions: [_,_]}, _b = %Tensor{dimensions: [_,_]}) do
-    raise Tensor.ArithmeticError, "Cannot compute dot product if the width of matrix `a` does not match the height of matrix `b`!"
+    raise Tensor.ArithmeticError, "Cannot compute Matrix.product if the width of matrix `a` does not match the height of matrix `b`!"
   end
 
+  @doc """
+  Calculates the product of `matrix` with `matrix`, `exponent` times.
+  If `exponent` == 0, then the result will be the identity matrix with the same dimensions as the given matrix. 
+
+  This is calculated using the fast [exponentiation by squaring](https://en.wikipedia.org/wiki/Exponentiation_by_squaring) algorithm.
+  """
+  def power(matrix, exponent)
+
+  def power(matrix = %Tensor{dimensions: [a,a]}, negative_number) when negative_number < 0 do
+    product(Matrix.identity_matrix(-1, a), power(matrix, -negative_number))
+  end
+
+  def power(matrix = %Tensor{dimensions: [a,a]}, 0), do: Matrix.identity_matrix(a)
+  def power(matrix = %Tensor{dimensions: [a,a]}, 1), do: matrix
+
+  def power(matrix = %Tensor{dimensions: [a,a]}, exponent) when rem(exponent, 2) == 0 do
+    power(product(matrix, matrix), Kernel.div(exponent, 2))
+  end
+
+  def power(matrix = %Tensor{dimensions: [a,a]}, exponent) when rem(exponent, 2) == 1 do
+    product(matrix, power(product(matrix, matrix), Kernel.div(exponent, 2)))
+  end
+
+  def power(matrix = %Tensor{dimensions: [_,_]}) do
+    raise Tensor.ArithmeticError, "Cannot compute Matrix.power with non-square matrices"
+  end
+
+
 end
 

lib/tensor.ex

@@ -155,16 +155,16 @@ defmodule Tensor do
 
       iex> mat = Matrix.new([[1,2],[3,4]], 2,2)   
       iex> {vector, mat2} = Tensor.pop(mat, 0)   
-      iex> inspect(vector)
-      "#Vector-(2)[1, 2]"
+      iex> vector
+      #Vector<(2)[1, 2]>
       iex> inspect(mat2)
-      "#Matrix-(2×2)
+      "#Matrix<(2×2)
       ┌                 ┐
       │       0,       0│
       │       3,       4│
       └                 ┘
+      >
       "
-
   """
   @spec pop(tensor, integer, any) :: { tensor | any, tensor}
   def pop(tensor, index, default \\ nil)

lib/tensor/inspect.ex

@@ -1,8 +1,9 @@
 defmodule Tensor.Inspect do
   def inspect(tensor, _opts) do
     """
-    #Tensor(#{dimension_string(tensor)})
+    #Tensor<(#{dimension_string(tensor)})
     #{inspect_tensor_contents(tensor)}
+    >
     """
   end
 

lib/vector.ex

@@ -3,7 +3,7 @@ defmodule Vector do
   defmodule Inspect do
     @doc false
     def inspect(vector, _opts) do
-      "#Vector-(#{Tensor.Inspect.dimension_string(vector)})#{inspect Vector.to_list(vector)}"
+      "#Vector<(#{Tensor.Inspect.dimension_string(vector)})#{inspect Vector.to_list(vector)}>"
     end
   end
 

mix.exs

@@ -3,7 +3,7 @@ defmodule Tensor.Mixfile do
 
   def project do
     [app: :tensor,
-     version: "0.7.0",
+     version: "0.7.1",
      elixir: "~> 1.3",
      build_embedded: Mix.env == :prod,
      start_permanent: Mix.env == :prod,

test/matrix_test.exs

@@ -9,22 +9,24 @@ defmodule MatrixTest do
   test "Inspect" do
     matrix = Matrix.new([[1,2],[3,4]], 2,2)
     assert Inspect.inspect(matrix, []) == """
-    #Matrix-(2×2)
+    #Matrix<(2×2)
     ┌                 ┐
     │       1,       2│
     │       3,       4│
     └                 ┘
+    >
     """
   end
 
   test "identity_matrix" do
     inspect Matrix.identity_matrix(3) =="""
-    #Matrix-(3×3)
+    #Matrix<(3×3)
     ┌                          ┐
     │       1,       0,       0│
     │       0,       1,       0│
     │       0,       0,       1│
     └                          ┘
+    >
     """
   end
 
@@ -50,11 +52,12 @@ defmodule MatrixTest do
     m1 = Matrix.new([[2,3,4],[1,0,0]], 2,3)
     m2 = Matrix.new([[0,1000],[1,100],[0,10]], 3,2)
     assert Matrix.product(m1, m2) |> inspect == """
-    #Matrix-(2×2)
+    #Matrix<(2×2)
     ┌                 ┐
     │       3,    2340│
     │       0,    1000│
     └                 ┘
+    >
     """
   end
 
@@ -82,7 +85,7 @@ defmodule MatrixTest do
     matrix = Matrix.new(board_as_list, 8,8)
     assert inspect(matrix) == 
     """
-    #Matrix-(8×8)
+    #Matrix<(8×8)
     ┌                                                                       ┐
     │     "♜",     "♞",     "♝",     "♛",     "♚",     "♝",     "♞",     "♜"│
     │     "♟",     "♟",     "♟",     "♟",     "♟",     "♟",     "♟",     "♟"│
@@ -93,6 +96,7 @@ defmodule MatrixTest do
     │     "♙",     "♙",     "♙",     "♙",     "♙",     "♙",     "♙",     "♙"│
     │     "♖",     "♘",     "♗",     "♕",     "♔",     "♗",     "♘",     "♖"│
     └                                                                       ┘
+    >
     """
 
   end