[Sparse] Support converson to/from torch sparse tensor.

dgl_sparse/include/sparse/sparse_matrix.h

@@ -79,15 +79,14 @@ class SparseMatrix : public torch::CustomClassHolder {
 
   /**
    * @brief Create a SparseMatrix from tensors in COO format.
-   * @param row Row indices of the COO.
-   * @param col Column indices of the COO.
+   * @param indices COO coordinates with shape (2, nnz).
    * @param value Values of the sparse matrix.
    * @param shape Shape of the sparse matrix.
    *
    * @return SparseMatrix
    */
   static c10::intrusive_ptr<SparseMatrix> FromCOO(
-      torch::Tensor row, torch::Tensor col, torch::Tensor value,
+      torch::Tensor indices, torch::Tensor value,
       const std::vector<int64_t>& shape);
 
   /**
@@ -153,6 +152,8 @@ class SparseMatrix : public torch::CustomClassHolder {
 
   /** @return {row, col} tensors in the COO format. */
   std::tuple<torch::Tensor, torch::Tensor> COOTensors();
+  /** @return Stacked row and col tensors in the COO format. */
+  torch::Tensor Indices();
   /** @return {row, col, value_indices} tensors in the CSR format. */
   std::tuple<torch::Tensor, torch::Tensor, torch::optional<torch::Tensor>>
   CSRTensors();

dgl_sparse/src/elemenwise_op.cc

@@ -22,19 +22,10 @@ c10::intrusive_ptr<SparseMatrix> SpSpAdd(
     const c10::intrusive_ptr<SparseMatrix>& A,
     const c10::intrusive_ptr<SparseMatrix>& B) {
   ElementwiseOpSanityCheck(A, B);
-  torch::Tensor sum;
-  {
-    // TODO(#5145) This is a workaround to reduce peak memory usage. It is no
-    // longer needed after we address #5145.
-    auto torch_A = COOToTorchCOO(A->COOPtr(), A->value());
-    auto torch_B = COOToTorchCOO(B->COOPtr(), B->value());
-    sum = torch_A + torch_B;
-  }
-  sum = sum.coalesce();
-  auto indices = sum.indices();
-  auto row = indices[0];
-  auto col = indices[1];
-  return SparseMatrix::FromCOO(row, col, sum.values(), A->shape());
+  auto torch_A = COOToTorchCOO(A->COOPtr(), A->value());
+  auto torch_B = COOToTorchCOO(B->COOPtr(), B->value());
+  auto sum = (torch_A + torch_B).coalesce();
+  return SparseMatrix::FromCOO(sum.indices(), sum.values(), A->shape());
 }
 
 }  // namespace sparse

dgl_sparse/src/python_binding.cc

@@ -27,6 +27,7 @@ TORCH_LIBRARY(dgl_sparse, m) {
       .def("device", &SparseMatrix::device)
       .def("shape", &SparseMatrix::shape)
       .def("coo", &SparseMatrix::COOTensors)
+      .def("indices", &SparseMatrix::Indices)
       .def("csr", &SparseMatrix::CSRTensors)
       .def("csc", &SparseMatrix::CSCTensors)
       .def("transpose", &SparseMatrix::Transpose)

dgl_sparse/src/sparse_matrix.cc

@@ -72,10 +72,10 @@ c10::intrusive_ptr<SparseMatrix> SparseMatrix::FromCSCPointer(
 }
 
 c10::intrusive_ptr<SparseMatrix> SparseMatrix::FromCOO(
-    torch::Tensor row, torch::Tensor col, torch::Tensor value,
+    torch::Tensor indices, torch::Tensor value,
     const std::vector<int64_t>& shape) {
-  auto coo = std::make_shared<COO>(
-      COO{shape[0], shape[1], torch::stack({row, col}), false, false});
+  auto coo =
+      std::make_shared<COO>(COO{shape[0], shape[1], indices, false, false});
   return SparseMatrix::FromCOOPointer(coo, value, shape);
 }
 
@@ -138,10 +138,14 @@ std::shared_ptr<CSR> SparseMatrix::CSCPtr() {
 
 std::tuple<torch::Tensor, torch::Tensor> SparseMatrix::COOTensors() {
   auto coo = COOPtr();
-  auto val = value();
   return std::make_tuple(coo->indices.index({0}), coo->indices.index({1}));
 }
 
+torch::Tensor SparseMatrix::Indices() {
+  auto coo = COOPtr();
+  return coo->indices;
+}
+
 std::tuple<torch::Tensor, torch::Tensor, torch::optional<torch::Tensor>>
 SparseMatrix::CSRTensors() {
   auto csr = CSRPtr();

dgl_sparse/src/sparse_matrix_coalesce.cc

@@ -17,10 +17,8 @@ namespace sparse {
 c10::intrusive_ptr<SparseMatrix> SparseMatrix::Coalesce() {
   auto torch_coo = COOToTorchCOO(this->COOPtr(), this->value());
   auto coalesced_coo = torch_coo.coalesce();
-  torch::Tensor indices = coalesced_coo.indices();
-  torch::Tensor row = indices[0];
-  torch::Tensor col = indices[1];
-  return SparseMatrix::FromCOO(row, col, coalesced_coo.values(), this->shape());
+  return SparseMatrix::FromCOO(
+      coalesced_coo.indices(), coalesced_coo.values(), this->shape());
 }
 
 bool SparseMatrix::HasDuplicate() {

python/dgl/sparse/sparse_matrix.py

@@ -109,12 +109,35 @@ def coo(self) -> Tuple[torch.Tensor, torch.Tensor]:
         --------
 
         >>> indices = torch.tensor([[1, 2, 1], [2, 4, 3]])
-        >>> A = from_coo(dst, src)
+        >>> A = dglsp.spmatrix(indices)
         >>> A.coo()
         (tensor([1, 2, 1]), tensor([2, 4, 3]))
         """
         return self.c_sparse_matrix.coo()
 
+    def indices(self) -> torch.Tensor:
+        r"""Returns the coordinate list (COO) representation in one tensor with
+        shape ``(2, nnz)``.
+
+        See `COO in Wikipedia <https://en.wikipedia.org/wiki/
+        Sparse_matrix#Coordinate_list_(COO)>`_.
+
+        Returns
+        -------
+        torch.Tensor
+            Stacked COO tensor with shape ``(2, nnz)``.
+
+        Examples
+        --------
+
+        >>> indices = torch.tensor([[1, 2, 1], [2, 4, 3]])
+        >>> A = dglsp.spmatrix(indices)
+        >>> A.indices()
+        tensor([[1, 2, 1],
+                [2, 4, 3]])
+        """
+        return self.c_sparse_matrix.indices()
+
     def csr(self) -> Tuple[torch.Tensor, torch.Tensor, torch.Tensor]:
         r"""Returns the compressed sparse row (CSR) representation of the sparse
         matrix.
@@ -140,7 +163,7 @@ def csr(self) -> Tuple[torch.Tensor, torch.Tensor, torch.Tensor]:
         --------
 
         >>> indices = torch.tensor([[1, 2, 1], [2, 4, 3]])
-        >>> A = from_coo(dst, src)
+        >>> A = dglsp.spmatrix(indices)
         >>> A.csr()
         (tensor([0, 0, 2, 3]), tensor([2, 3, 4]), tensor([0, 2, 1]))
         """
@@ -171,7 +194,7 @@ def csc(self) -> Tuple[torch.Tensor, torch.Tensor, torch.Tensor]:
         --------
 
         >>> indices = torch.tensor([[1, 2, 1], [2, 4, 3]])
-        >>> A = from_coo(dst, src)
+        >>> A = dglsp.spmatrix(indices)
         >>> A.csc()
         (tensor([0, 0, 0, 1, 2, 3]), tensor([1, 1, 2]), tensor([0, 2, 1]))
         """
@@ -521,7 +544,18 @@ def spmatrix(
                                 [3., 3.]]),
                  shape=(3, 5), nnz=3, val_size=(2,))
     """
-    return from_coo(indices[0], indices[1], val, shape)
+    if shape is None:
+        shape = (
+            torch.max(indices[0]).item() + 1,
+            torch.max(indices[1]).item() + 1,
+        )
+    if val is None:
+        val = torch.ones(indices.shape[1]).to(indices.device)
+
+    assert (
+        val.dim() <= 2
+    ), "The values of a SparseMatrix can only be scalars or vectors."
+    return SparseMatrix(torch.ops.dgl_sparse.from_coo(indices, val, shape))
 
 
 def from_coo(
@@ -599,16 +633,8 @@ def from_coo(
                                 [3., 3.]]),
                  shape=(3, 5), nnz=3, val_size=(2,))
     """
-    if shape is None:
-        shape = (torch.max(row).item() + 1, torch.max(col).item() + 1)
-    if val is None:
-        val = torch.ones(row.shape[0]).to(row.device)
-
-    assert (
-        val.dim() <= 2
-    ), "The values of a SparseMatrix can only be scalars or vectors."
-
-    return SparseMatrix(torch.ops.dgl_sparse.from_coo(row, col, val, shape))
+    assert row.shape[0] == col.shape[0]
+    return spmatrix(torch.stack([row, col]), val, shape)
 
 
 def from_csr(
@@ -833,6 +859,168 @@ def val_like(mat: SparseMatrix, val: torch.Tensor) -> SparseMatrix:
     return SparseMatrix(torch.ops.dgl_sparse.val_like(mat.c_sparse_matrix, val))
 
 
+def from_torch_sparse(torch_sparse_tensor: torch.Tensor) -> SparseMatrix:
+    """Creates a sparse matrix from a torch sparse tensor, which can have coo,
+    csr, or csc layout.
+
+    Parameters
+    ----------
+    torch_sparse_tensor : torch.Tensor
+        Torch sparse tensor
+
+    Returns
+    -------
+    SparseMatrix
+        Sparse matrix
+
+    Examples
+    --------
+
+    >>> indices = torch.tensor([[1, 1, 2], [2, 4, 3]])
+    >>> val = torch.ones(3)
+    >>> torch_coo = torch.sparse_coo_tensor(indices, val)
+    >>> dglsp.from_torch_sparse(torch_coo)
+    SparseMatrix(indices=tensor([[1, 1, 2],
+                                 [2, 4, 3]]),
+                 values=tensor([1., 1., 1.]),
+                 shape=(3, 5), nnz=3)
+    """
+    if torch_sparse_tensor.layout == torch.sparse_coo:
+        # Use ._indices() and ._values() to access uncoalesced indices and
+        # values.
+        return spmatrix(
+            torch_sparse_tensor._indices(),
+            torch_sparse_tensor._values(),
+            torch_sparse_tensor.shape[:2],
+        )
+    elif torch_sparse_tensor.layout == torch.sparse_csr:
+        return from_csr(
+            torch_sparse_tensor.crow_indices(),
+            torch_sparse_tensor.col_indices(),
+            torch_sparse_tensor.values(),
+            torch_sparse_tensor.shape[:2],
+        )
+    elif torch_sparse_tensor.layout == torch.sparse_csc:
+        return from_csc(
+            torch_sparse_tensor.ccol_indices(),
+            torch_sparse_tensor.row_indices(),
+            torch_sparse_tensor.values(),
+            torch_sparse_tensor.shape[:2],
+        )
+    else:
+        assert False, (
+            f"Cannot convert Pytorch sparse tensor"
+            f"{torch_sparse_tensor} to DGL sparse."
+        )
+
+
+def to_torch_sparse_coo(spmat: SparseMatrix) -> torch.Tensor:
+    """Creates a torch sparse coo tensor from a sparse matrix.
+
+    Parameters
+    ----------
+    spmat : SparseMatrix
+        Sparse matrix
+
+    Returns
+    -------
+    torch.Tensor
+        torch tensor with torch.sparse_coo layout
+
+    Examples
+    --------
+
+    >>> indices = torch.tensor([[1, 1, 2], [2, 4, 3]])
+    >>> val = torch.ones(3)
+    >>> spmat = dglsp.spmatrix(indices, val)
+    >>> dglsp.to_torch_sparse_coo(spmat)
+    tensor(indices=tensor([[1, 1, 2],
+                           [2, 4, 3]]),
+           values=tensor([1., 1., 1.]),
+           size=(3, 5), nnz=3, layout=torch.sparse_coo)
+    """
+    shape = spmat.shape
+    if spmat.val.dim() > 1:
+        shape += spmat.val.shape[1:]
+    return torch.sparse_coo_tensor(spmat.indices(), spmat.val, shape)
+
+
+def to_torch_sparse_csr(spmat: SparseMatrix) -> torch.Tensor:
+    """Creates a torch sparse csr tensor from a sparse matrix.
+
+    Note that converting a sparse matrix to torch csr tensor could change the
+    order of non-zero values.
+
+    Parameters
+    ----------
+    spmat : SparseMatrix
+        Sparse matrix
+
+    Returns
+    -------
+    torch.Tensor
+        Torch tensor with torch.sparse_csr layout
+
+    Examples
+    --------
+
+    >>> indices = torch.tensor([[1, 2, 1], [2, 4, 3]])
+    >>> val = torch.arange(3)
+    >>> spmat = dglsp.spmatrix(indices, val)
+    >>> dglsp.to_torch_sparse_csr(spmat)
+    tensor(crow_indices=tensor([0, 0, 2, 3]),
+           col_indices=tensor([2, 3, 4]),
+           values=tensor([0, 2, 1]), size=(3, 5), nnz=3,
+           layout=torch.sparse_csr)
+    """
+    shape = spmat.shape
+    if spmat.val.dim() > 1:
+        shape += spmat.val.shape[1:]
+    indptr, indices, value_indices = spmat.csr()
+    val = spmat.val
+    if value_indices is not None:
+        val = val[value_indices]
+    return torch.sparse_csr_tensor(indptr, indices, val, shape)
+
+
+def to_torch_sparse_csc(spmat: SparseMatrix) -> torch.Tensor:
+    """Creates a torch sparse csc tensor from a sparse matrix.
+
+    Note that converting a sparse matrix to torch csc tensor could change the
+    order of non-zero values.
+
+    Parameters
+    ----------
+    spmat : SparseMatrix
+        Sparse matrix
+
+    Returns
+    -------
+    torch.Tensor
+        Torch tensor with torch.sparse_csc layout
+
+    Examples
+    --------
+
+    >>> indices = torch.tensor([[1, 2, 1], [2, 4, 3]])
+    >>> val = torch.arange(3)
+    >>> spmat = dglsp.spmatrix(indices, val)
+    >>> dglsp.to_torch_sparse_csc(spmat)
+    tensor(ccol_indices=tensor([0, 0, 0, 1, 2, 3]),
+           row_indices=tensor([1, 1, 2]),
+           values=tensor([0, 2, 1]), size=(3, 5), nnz=3,
+           layout=torch.sparse_csc)
+    """
+    shape = spmat.shape
+    if spmat.val.dim() > 1:
+        shape += spmat.val.shape[1:]
+    indptr, indices, value_indices = spmat.csc()
+    val = spmat.val
+    if value_indices is not None:
+        val = val[value_indices]
+    return torch.sparse_csc_tensor(indptr, indices, val, shape)
+
+
 def _sparse_matrix_str(spmat: SparseMatrix) -> str:
     """Internal function for converting a sparse matrix to string
     representation.