Correct an error in the value_at function.

Add some doctests for the value_at function.

diff --git a/src/FunctionValues.hs b/src/FunctionValues.hs
index 8eb5bdb0d375ffdfe72eabb81097cc99c121e563..895f9253a42506398c5594a3bd8b864baa32099a 100644 (file)
--- a/src/FunctionValues.hs
+++ b/src/FunctionValues.hs
@@ -164,14 +164,29 @@ eval f (Quotient x y) = (eval f x) / (eval f y)
 --   coordinates (i,j,k), and returns the value at (i,j,k) in the
 --   supplied list. If there is no such value, we choose a nearby
 --   point and use its value.
+--
+--   Examples:
+--
+--   >>> value_at Examples.trilinear 0 0 0
+--   1.0
+--
+--   >>> value_at Examples.trilinear (-1) 0 0
+--   1.0
+--
+--   >>> value_at Examples.trilinear 0 0 4
+--   1.0
+--
+--   >>> value_at Examples.trilinear 1 3 0
+--   4.0
+--
 value_at :: Values3D -> Int -> Int -> Int -> Double
 value_at v3d i j k
          | i < 0 = value_at v3d 0 j k
          | j < 0 = value_at v3d i 0 k
          | k < 0 = value_at v3d i j 0
-         | xsize <= i = value_at v3d xsize j k
-         | ysize <= j = value_at v3d i ysize k
-         | zsize <= k = value_at v3d i j zsize
+         | xsize <= i = value_at v3d (xsize - 1) j k
+         | ysize <= j = value_at v3d i (ysize - 1) k
+         | zsize <= k = value_at v3d i j (zsize - 1)
          | otherwise = idx v3d i j k
   where
     (xsize, ysize, zsize) = dims v3d