From 7c2301797e35930298db9a6bff09eefdd4fbd577 Mon Sep 17 00:00:00 2001
From: Erik de Castro Lopo <erikd@mega-nerd.com>
Date: Thu, 10 Dec 2009 10:35:35 +0000
Subject: Add functions buildVector and buildMatrix.

Both take a size parameter(s) and a function that maps vector/matrix indices
to the values at that position.
---
 lib/Data/Packed/Matrix.hs | 17 ++++++++++++++++-
 lib/Data/Packed/Vector.hs | 13 ++++++++++++-
 2 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/lib/Data/Packed/Matrix.hs b/lib/Data/Packed/Matrix.hs
index ad0776e..6a6942d 100644
--- a/lib/Data/Packed/Matrix.hs
+++ b/lib/Data/Packed/Matrix.hs
@@ -19,7 +19,7 @@ module Data.Packed.Matrix (
     (><),
     trans,
     reshape, flatten,
-    fromLists, toLists,
+    fromLists, toLists, buildMatrix,
     (@@>),
     asRow, asColumn,
     fromRows, toRows, fromColumns, toColumns,
@@ -176,6 +176,21 @@ asRow v = reshape (dim v) v
 asColumn :: Element a => Vector a -> Matrix a
 asColumn v = reshape 1 v
 
+
+{- | creates a Matrix of the specified size using the supplied function to
+     to map the row/column position to the value at that row/column position.
+
+@> buildMatrix 3 4 (\ (r,c) -> fromIntegral r * fromIntegral c)
+(3><4)
+ [ 0.0, 0.0, 0.0, 0.0, 0.0
+ , 0.0, 1.0, 2.0, 3.0, 4.0
+ , 0.0, 2.0, 4.0, 6.0, 8.0]@
+-}
+buildMatrix :: Element a => Int -> Int -> ((Int, Int) -> a) -> Matrix a
+buildMatrix rc cc f =
+    fromLists $ map (\x -> map f x)
+    	$ map (\ ri -> map (\ ci -> (ri, ci)) [0 .. (cc - 1)]) [0 .. (rc - 1)]
+
 -----------------------------------------------------
 
 fromArray2D :: (Element e) => Array (Int, Int) e -> Matrix e
diff --git a/lib/Data/Packed/Vector.hs b/lib/Data/Packed/Vector.hs
index 21f51e5..457da71 100644
--- a/lib/Data/Packed/Vector.hs
+++ b/lib/Data/Packed/Vector.hs
@@ -14,7 +14,7 @@
 
 module Data.Packed.Vector (
     Vector,
-    fromList, (|>), toList,
+    fromList, (|>), toList, buildVector,
     dim, (@>),
     subVector, join,
     constant, linspace,
@@ -59,3 +59,14 @@ vectorMinIndex = round . toScalarR MinIdx
 constant :: Element a => a -> Int -> Vector a
 -- constant x n = runSTVector (newVector x n)
 constant = constantD -- about 2x faster
+
+{- | creates a Vector of the specified length using the supplied function to
+     to map the index to the value at that index.
+
+@> buildVector 4 fromIntegral
+4 |> [0.0,1.0,2.0,3.0]@
+
+-}
+buildVector :: Element a => Int -> (Int -> a) -> Vector a
+buildVector len f =
+    fromList $ map f [0 .. (len - 1)]
-- 
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