treat zero dimension like numpy does

src/dimension/broadcast.rs

@@ -23,15 +23,13 @@ where
     // (https://docs.scipy.org/doc/numpy/user/basics.broadcasting.html#general-broadcasting-rules).
     //
     // Zero dimension element is not in the original rules of broadcasting.
-    // We currently treat it as the same as 1. Especially, when one side is
-    // zero with one side is empty, or both sides are zero, the result will
-    // remain zero.
+    // We currently treat it like any other number greater than 1. As numpy does.
     for i in 0..shape1.ndim() {
         out_slice[i] = s1[i];
     }
     for i in 0..shape2.ndim() {
-        if out_slice[i + k] != s2[i] && s2[i] != 0 {
-            if out_slice[i + k] <= 1 {
+        if out_slice[i + k] != s2[i] {
+            if out_slice[i + k] == 1 {
                 out_slice[i + k] = s2[i]
             } else if s2[i] != 1 {
                 return Err(from_kind(ErrorKind::IncompatibleShape));

src/numeric/impl_numeric.rs

@@ -243,7 +243,7 @@ where
     /// **Panics** if `axis` is out of bounds.
     pub fn sum_axis(&self, axis: Axis) -> Array<A, D::Smaller>
     where
-        A: Copy + Zero + Add<Output = A>,
+        A: Clone + Zero + Add<Output = A>,
         D: RemoveAxis,
     {
         let n = self.len_of(axis);
@@ -285,7 +285,7 @@ where
     /// ```
     pub fn mean_axis(&self, axis: Axis) -> Option<Array<A, D::Smaller>>
     where
-        A: Copy + Zero + FromPrimitive + Add<Output = A> + Div<Output = A>,
+        A: Clone + Zero + FromPrimitive + Add<Output = A> + Div<Output = A>,
         D: RemoveAxis,
     {
         let axis_length = self.len_of(axis);

tests/array.rs

@@ -1589,19 +1589,19 @@ fn test_broadcast_shape() {
     test_co(
         &Dim([2, 1, 2]).into_dyn(),
         &Dim(0),
-        Ok(Dim([2, 1, 2]).into_dyn()),
+        Err(ShapeError::from_kind(ErrorKind::IncompatibleShape)),
     );
     test_co(
         &Dim([2, 1, 1]),
-        &Dim([0, 0, 0, 3, 4]),
+        &Dim([0, 0, 1, 3, 4]),
         Ok(Dim([0, 0, 2, 3, 4])),
     );
     test_co(&Dim([0]), &Dim([0, 0, 0]), Ok(Dim([0, 0, 0])));
-    test_co(&Dim(1), &Dim([1, 0, 0]), Ok(Dim([1, 0, 1])));
+    test_co(&Dim(1), &Dim([1, 0, 0]), Ok(Dim([1, 0, 0])));
     test_co(
         &Dim([1, 3, 0, 1, 1]),
         &Dim([1, 2, 3, 1]),
-        Ok(Dim([1, 3, 2, 3, 1])),
+        Err(ShapeError::from_kind(ErrorKind::IncompatibleShape)),
     );
 }