Merge pull request #45 from hanslovsky/partial-derivative-bug

Fix #42

Author: tpietzsch

src/main/java/net/imglib2/algorithm/gradient/PartialDerivative.java

@@ -180,8 +180,8 @@ public static < T extends NumericType< T > > void gradientCentralDifference( fin
 			shiftback[ d ] = min[ d ] - max[ d ];
 
 		final RandomAccess< T > result = gradient.randomAccess();
-		final RandomAccess< T > back = source.randomAccess( Intervals.translate( gradient, 1, dimension ) );
-		final RandomAccess< T > front = source.randomAccess( Intervals.translate( gradient, -1, dimension ) );
+		final RandomAccess< T > back = source.randomAccess( Intervals.translate( gradient, -1, dimension ) );
+		final RandomAccess< T > front = source.randomAccess( Intervals.translate( gradient, 1, dimension ) );
 
 		result.setPosition( min );
 		back.setPosition( min );