From: Michael Orlitzky <michael@orlitzky.com>
Date: Sun, 2 Feb 2014 16:33:03 +0000 (-0500)
Subject: New function: Linear.Matrix.identity_matrix.
X-Git-Url: https://gitweb.michael.orlitzky.com/?a=commitdiff_plain;h=d9089a0f219795b9f4ff7f8b5576cef678fbe36d;p=numerical-analysis.git

New function: Linear.Matrix.identity_matrix.
---

diff --git a/src/Linear/Matrix.hs b/src/Linear/Matrix.hs
index c48f722..c0f56b3 100644
--- a/src/Linear/Matrix.hs
+++ b/src/Linear/Matrix.hs
@@ -213,6 +213,18 @@ construct lambda = Mat $ generate make_row
     make_row i = generate (lambda i)
 
 
+-- | Create an identity matrix with the right dimensions.
+--
+--   Examples:
+--
+--   >>> identity_matrix :: Mat3 Int
+--   ((1,0,0),(0,1,0),(0,0,1))
+--   >>> identity_matrix :: Mat3 Double
+--   ((1.0,0.0,0.0),(0.0,1.0,0.0),(0.0,0.0,1.0))
+--
+identity_matrix :: (Arity m, Ring.C a) => Mat m m a
+identity_matrix =
+  construct (\i j -> if i == j then (fromInteger 1) else (fromInteger 0))
 
 -- | Given a positive-definite matrix @m@, computes the
 --   upper-triangular matrix @r@ with (transpose r)*r == m and all