Fix the definition of cube_at; it had the 'x' and 'z' axes flipped.

diff --git a/src/Cube.hs b/src/Cube.hs
index d741f490c6e7499a309b991c0e5d3ba0a9c6cd55..301128116eb0f9127c5e5012fb5b0a4c9f5552df 100644 (file)
--- a/src/Cube.hs
+++ b/src/Cube.hs
@@ -38,8 +38,7 @@ instance Show Cube where
 empty_cube :: Cube
 empty_cube = Cube empty_grid 0 0 0 0
 
--- TODO: The paper considers 'i' to be the front/back direction,
--- whereas I have it in the left/right direction.
+
 instance Gridded Cube where
     back c = cube_at (grid c) ((i c) + 1) (j c) (k c)
     down c = cube_at (grid c) (i c) (j c) ((k c) - 1)
@@ -146,11 +145,14 @@ instance Fractional Cube where
 
     fromRational q = empty_cube { datum = fromRational q }
 
--- | Constructs a cube, switching the i and k axes.
+-- | Constructs a cube, switching the x and z axes.
 reverse_cube :: Grid -> Int -> Int -> Int -> Double -> Cube
 reverse_cube g k' j' i' = Cube g i' j' k'
 
 
+-- | Return the cube corresponding to the grid point i,j,k. The list
+--   of cubes is stored as [z][y][x] but we'll be requesting it by
+--   [x][y][z] so we flip the indices in the last line.
 cube_at :: Grid -> Int -> Int -> Int -> Cube
 cube_at g i' j' k'
         | i' >= length (function_values g) = Cube g i' j' k' 0
@@ -160,7 +162,8 @@ cube_at g i' j' k'
         | k' >= length (((function_values g) !! i') !! j') = Cube g i' j' k' 0
         | k' < 0                                          = Cube g i' j' k' 0
         | otherwise =
-            Cube g i' j' k' ((((function_values g) !! i') !! j') !! k')
+            (((cubes g) !! k') !! j') !! i'
+
 
 -- These next three functions basically form a 'for' loop, looping
 -- through the xs, ys, and zs in that order.