Addressing feedback.

Author: cgranade

src/Simulation/qdk_sim_rs/README.md

@@ -145,3 +145,4 @@ TODO
 - Too many APIs `panic!` or `unwrap`, and need replaced with `Result` returns instead.
 
 # Crate features
+<!-- Note that this section is filled in automatically by document-features. -->

src/Simulation/qdk_sim_rs/src/error.rs

@@ -11,8 +11,8 @@ use thiserror::Error;
 /// Represents errors that can occur during linear algebra operations.
 #[derive(Debug, Diagnostic, Error)]
 pub enum QdkSimError {
-    // NB: As a design note, these should be eliminated before stabilizing the
-    //     API for this simulator crate.
+    // NB: As a design note, please consider if a more specific error is better
+    //     suited for your usecase before returning `MiscError`.
     /// Raised on miscellaneous errors.
     #[error("{0}")]
     #[diagnostic(code(qdk_sim::other))]

src/Simulation/qdk_sim_rs/src/linalg/array_ext.rs

@@ -76,9 +76,9 @@ where
     D: Dimension + RemoveAxis,
 {
     fn swap_index_axis(&mut self, axis: Axis, idx_source: usize, idx_dest: usize) {
-        // TODO: Avoid copying both; this is needed currently to avoid mutably
-        //       borrowing something which has an outstanding immutable
-        //       borrow.
+        // TODO[perf]: Avoid copying both; this is needed currently to avoid mutably
+        //             borrowing something which has an outstanding immutable
+        //             borrow.
         let source = self.index_axis(axis, idx_source).clone().to_owned();
         let dest = self.index_axis(axis, idx_dest).clone().to_owned();
         self.index_axis_mut(axis, idx_source).assign(&dest);
@@ -88,7 +88,7 @@ where
 
 #[cfg(test)]
 mod tests {
-    use super::ArrayBaseMatrixExt;
+    use super::{ArrayBaseMatrixExt, ArrayBaseRemoveAxisExt};
     use ndarray::{array, Array2};
 
     #[test]
@@ -110,4 +110,20 @@ mod tests {
             array![[6.0, 0.0, 0.0], [2.0, 12.0, 0.0], [4.0, 15.0, 3.0]]
         );
     }
+
+    #[test]
+    fn swap_index_axis_swaps_rows_correctly() {
+        let mut mtx = array![[6.0, 18.0, 3.0], [2.0, 12.0, 1.0], [4.0, 15.0, 3.0]];
+        mtx.swap_index_axis(ndarray::Axis(0), 1, 2);
+        let expected = array![[6.0, 18.0, 3.0], [4.0, 15.0, 3.0], [2.0, 12.0, 1.0]];
+        assert_eq!(mtx, expected);
+    }
+
+    #[test]
+    fn swap_index_axis_swaps_columns_correctly() {
+        let mut mtx = array![[6.0, 18.0, 3.0], [2.0, 12.0, 1.0], [4.0, 15.0, 3.0]];
+        mtx.swap_index_axis(ndarray::Axis(1), 1, 2);
+        let expected = array![[6.0, 3.0, 18.0], [2.0, 1.0, 12.0], [4.0, 3.0, 15.0]];
+        assert_eq!(mtx, expected);
+    }
 }