add benches for sparse matrix multiplication

sbp/benches/sbpoperators.rs

@@ -45,6 +45,72 @@ fn performance_benchmark(c: &mut Criterion) {
         b.iter(|| operators::SBP8.diffeta(x.view(), res.view_mut()))
     });
 
+    #[cfg(feature = "sparse")]
+    {
+        use sbp::utils::kronecker_product;
+
+        fn make_operators(
+            op: impl SbpOperator2d,
+            nx: usize,
+            ny: usize,
+        ) -> (sprs::CsMat<Float>, sprs::CsMat<Float>) {
+            let dx = op.op_xi().diff_matrix(nx);
+            let dx = kronecker_product(sprs::CsMat::eye(ny).view(), dx.view());
+
+            let dy = op.op_eta().diff_matrix(ny);
+            let dy = kronecker_product(dy.view(), sprs::CsMat::eye(nx).view());
+
+            (dy, dx)
+        }
+
+        {
+            let (dy, dx) = make_operators(operators::Upwind4, w, h);
+            group.bench_function("upwind4 diffxi matrix", |b| {
+                let mut res = ndarray::Array2::zeros(x.raw_dim());
+                b.iter(|| {
+                    sprs::prod::mul_acc_mat_vec_csr(
+                        dx.view(),
+                        x.as_slice().unwrap(),
+                        res.as_slice_mut().unwrap(),
+                    )
+                })
+            });
+            group.bench_function("upwind4 diffeta matrix", |b| {
+                let mut res = ndarray::Array2::zeros(x.raw_dim());
+                b.iter(|| {
+                    sprs::prod::mul_acc_mat_vec_csr(
+                        dy.view(),
+                        x.as_slice().unwrap(),
+                        res.as_slice_mut().unwrap(),
+                    )
+                })
+            });
+        }
+        {
+            let (dy, dx) = make_operators(operators::Upwind9, w, h);
+            group.bench_function("upwind9 diffxi matrix", |b| {
+                let mut res = ndarray::Array2::zeros(x.raw_dim());
+                b.iter(|| {
+                    sprs::prod::mul_acc_mat_vec_csr(
+                        dx.view(),
+                        x.as_slice().unwrap(),
+                        res.as_slice_mut().unwrap(),
+                    )
+                })
+            });
+            group.bench_function("upwind9 diffeta matrix", |b| {
+                let mut res = ndarray::Array2::zeros(x.raw_dim());
+                b.iter(|| {
+                    sprs::prod::mul_acc_mat_vec_csr(
+                        dy.view(),
+                        x.as_slice().unwrap(),
+                        res.as_slice_mut().unwrap(),
+                    )
+                })
+            });
+        }
+    }
+
     group.finish();
 }