From 41ce9a23dfc4321618322bc3c901b9203ebf67e2 Mon Sep 17 00:00:00 2001
From: Andreas Longva <andreas.b.longva@gmail.com>
Date: Mon, 23 Nov 2020 15:58:02 +0100
Subject: [PATCH] Remove CooMatrix::to_dense() and `Scalar` trait bound, add
 ::nnz()

---
 nalgebra-sparse/src/coo.rs              | 32 ++++++++-----------------
 nalgebra-sparse/tests/unit_tests/coo.rs |  6 ++---
 nalgebra-sparse/tests/unit_tests/ops.rs |  4 ++--
 3 files changed, 15 insertions(+), 27 deletions(-)

diff --git a/nalgebra-sparse/src/coo.rs b/nalgebra-sparse/src/coo.rs
index 8206cb09..43662da3 100644
--- a/nalgebra-sparse/src/coo.rs
+++ b/nalgebra-sparse/src/coo.rs
@@ -1,8 +1,6 @@
 //! An implementation of the COO sparse matrix format.
 
 use crate::SparseFormatError;
-use nalgebra::{ClosedAdd, DMatrix, Scalar};
-use num_traits::Zero;
 
 /// A COO representation of a sparse matrix.
 ///
@@ -47,8 +45,6 @@ pub struct CooMatrix<T> {
 }
 
 impl<T> CooMatrix<T>
-where
-    T: Scalar,
 {
     /// Construct a zero COO matrix of the given dimensions.
     ///
@@ -146,6 +142,16 @@ where
         self.ncols
     }
 
+    /// The number of explicitly stored entries in the matrix.
+    ///
+    /// This number *includes* duplicate entries. For example, if the `CooMatrix` contains duplicate
+    /// entries, then it may have a different number of non-zeros as reported by `nnz()` compared
+    /// to its CSR representation.
+    #[inline]
+    pub fn nnz(&self) -> usize {
+        self.values.len()
+    }
+
     /// The row indices of the explicitly stored entries.
     pub fn row_indices(&self) -> &[usize] {
         &self.row_indices
@@ -182,22 +188,4 @@ where
     pub fn disassemble(self) -> (Vec<usize>, Vec<usize>, Vec<T>) {
         (self.row_indices, self.col_indices, self.values)
     }
-
-    /// Construct the dense representation of the COO matrix.
-    ///
-    /// Duplicate entries are summed together.
-    ///
-    /// TODO: Remove?
-    pub fn to_dense(&self) -> DMatrix<T>
-    where
-        T: ClosedAdd + Zero,
-    {
-        let mut result = DMatrix::zeros(self.nrows, self.ncols);
-
-        for (i, j, v) in self.triplet_iter() {
-            result[(i, j)] += v.clone();
-        }
-
-        result
-    }
 }
diff --git a/nalgebra-sparse/tests/unit_tests/coo.rs b/nalgebra-sparse/tests/unit_tests/coo.rs
index 7bf0c05c..3373d89a 100644
--- a/nalgebra-sparse/tests/unit_tests/coo.rs
+++ b/nalgebra-sparse/tests/unit_tests/coo.rs
@@ -19,7 +19,7 @@ fn coo_construction_for_valid_data() {
         assert!(coo.col_indices().is_empty());
         assert!(coo.values().is_empty());
 
-        assert_eq!(coo.to_dense(), DMatrix::repeat(3, 2, 0));
+        assert_eq!(DMatrix::from(&coo), DMatrix::repeat(3, 2, 0));
     }
 
     {
@@ -51,7 +51,7 @@ fn coo_construction_for_valid_data() {
             0, 0, 3, 0, 0,
             0, 0, 0, 1, 0
         ]);
-        assert_eq!(coo.to_dense(), expected_dense);
+        assert_eq!(DMatrix::from(&coo), expected_dense);
     }
 
     {
@@ -83,7 +83,7 @@ fn coo_construction_for_valid_data() {
             0, 0, 8, 0, 0,
             0, 0, 0, 1, 0
         ]);
-        assert_eq!(coo.to_dense(), expected_dense);
+        assert_eq!(DMatrix::from(&coo), expected_dense);
     }
 }
 
diff --git a/nalgebra-sparse/tests/unit_tests/ops.rs b/nalgebra-sparse/tests/unit_tests/ops.rs
index a2c06b96..01df60b6 100644
--- a/nalgebra-sparse/tests/unit_tests/ops.rs
+++ b/nalgebra-sparse/tests/unit_tests/ops.rs
@@ -1,6 +1,6 @@
 use nalgebra_sparse::coo::CooMatrix;
 use nalgebra_sparse::ops::spmv_coo;
-use nalgebra::DVector;
+use nalgebra::{DVector, DMatrix};
 
 #[test]
 fn spmv_coo_agrees_with_dense_gemv() {
@@ -20,7 +20,7 @@ fn spmv_coo_agrees_with_dense_gemv() {
             let mut y_dense = y.clone();
             spmv_coo(beta, &mut y, alpha, &a, &x);
 
-            y_dense.gemv(alpha, &a.to_dense(), &x, beta);
+            y_dense.gemv(alpha, &DMatrix::from(&a), &x, beta);
 
             assert_eq!(y, y_dense);
         }