Use generic methods for * and / with a scalar (#43)

* Use generic methods for `*` and `/` with a scalar

* Fix errors with Metal

Author: albertomercurio

src/core.jl

@@ -32,13 +32,17 @@ function LinearAlgebra.lmul!(x::Number, A::AbstractGenericSparseArray)
     return A
 end
 
-function LinearAlgebra.rdiv!(A::AbstractGenericSparseArray, x::Number)
-    rdiv!(nonzeros(A), x)
+function LinearAlgebra.rdiv!(A::AbstractGenericSparseArray{Tv}, x::Number) where {Tv}
+    rmul!(A, inv(Tv(x)))
     return A
 end
 
 Base.:+(A::AbstractGenericSparseArray) = copy(A)
 
+Base.:*(α::Number, A::AbstractGenericSparseArray) = lmul!(α, copy(A))
+Base.:*(A::AbstractGenericSparseArray, α::Number) = rmul!(copy(A), α)
+Base.:(/)(A::AbstractGenericSparseArray, α::Number) = rdiv!(copy(A), α)
+
 Base.:*(A::AbstractGenericSparseArray, J::UniformScaling) = A * J.λ
 Base.:*(J::UniformScaling, A::AbstractGenericSparseArray) = J.λ * A
 

src/matrix_coo/matrix_coo.jl

@@ -104,18 +104,6 @@ function Base.zero(A::GenericSparseMatrixCOO)
     return GenericSparseMatrixCOO(A.m, A.n, rowind, colind, nzval)
 end
 
-function Base.:(*)(α::Number, A::GenericSparseMatrixCOO)
-    return GenericSparseMatrixCOO(
-        A.m,
-        A.n,
-        copy(getrowind(A)),
-        copy(getcolind(A)),
-        α .* nonzeros(A),
-    )
-end
-Base.:(*)(A::GenericSparseMatrixCOO, α::Number) = α * A
-Base.:(/)(A::GenericSparseMatrixCOO, α::Number) = (1 / α) * A
-
 function Base.:-(A::GenericSparseMatrixCOO)
     return GenericSparseMatrixCOO(A.m, A.n, copy(A.rowind), copy(A.colind), -A.nzval)
 end
@@ -392,8 +380,7 @@ function Base.:+(A::GenericSparseMatrixCOO, B::GenericSparseMatrixCOO)
     )
 
     C = GenericSparseMatrixCOO(m, n, rowind_C, colind_C, nzval_C)
-    dropzeros!(C)
-    return C
+    return dropzeros(C)
 end
 
 # Addition with transpose/adjoint support
@@ -511,8 +498,7 @@ for (wrapa, transa, conja, unwrapa, whereT1) in trans_adj_wrappers(:GenericSpars
             )
 
             C = GenericSparseMatrixCOO(m, n, rowind_C, colind_C, nzval_C)
-            dropzeros!(C)
-            return C
+            return dropzeros(C)
         end
 
         @eval function Base.:-(A::$TypeA, B::$TypeB) where {$(whereT1(:T1)), $(whereT2(:T2))}
@@ -820,6 +806,13 @@ function SparseArrays.dropzeros!(A::GenericSparseMatrixCOO)
         return A
     end
 
+    if total_nnz == 0
+        # All elements are zeros - some GPU backends (e.g., Metal) don't support
+        # resize to 0. Keep the stored zeros; users can use dropzeros() (non-mutating)
+        # which returns a new matrix with properly empty arrays.
+        return A
+    end
+
     # Allocate temporary arrays for new data
     new_rowind = similar(rowind, total_nnz)
     new_colind = similar(colind, total_nnz)

src/matrix_csc/matrix_csc.jl

@@ -85,18 +85,6 @@ function Base.zero(A::GenericSparseMatrixCSC)
     return GenericSparseMatrixCSC(A.m, A.n, colptr, rowval, nzval)
 end
 
-function Base.:(*)(α::Number, A::GenericSparseMatrixCSC)
-    return GenericSparseMatrixCSC(
-        A.m,
-        A.n,
-        copy(getcolptr(A)),
-        copy(rowvals(A)),
-        α .* nonzeros(A),
-    )
-end
-Base.:(*)(A::GenericSparseMatrixCSC, α::Number) = α * A
-Base.:(/)(A::GenericSparseMatrixCSC, α::Number) = (1 / α) * A
-
 function Base.:-(A::GenericSparseMatrixCSC)
     return GenericSparseMatrixCSC(A.m, A.n, copy(A.colptr), copy(A.rowval), -A.nzval)
 end
@@ -365,8 +353,7 @@ function Base.:+(A::GenericSparseMatrixCSC, B::GenericSparseMatrixCSC)
     )
 
     C = GenericSparseMatrixCSC(m, n, colptr_C, rowval_C, nzval_C)
-    dropzeros!(C)
-    return C
+    return dropzeros(C)
 end
 
 # Addition with transpose/adjoint support
@@ -662,6 +649,13 @@ function SparseArrays.dropzeros!(A::GenericSparseMatrixCSC)
     cumsum_nnz = _cumsum_AK(nnz_per_col)
     total_nnz = @allowscalar cumsum_nnz[end]
 
+    if total_nnz == 0
+        # All elements are zeros - some GPU backends (e.g., Metal) don't support
+        # resize to 0. Keep the stored zeros; users can use dropzeros() (non-mutating)
+        # which returns a new matrix with properly empty arrays.
+        return A
+    end
+
     # Allocate temporary arrays for new data
     new_colptr = similar(getcolptr(A))
     new_rowval = similar(rowvals(A), total_nnz)

src/matrix_csr/matrix_csr.jl

@@ -85,18 +85,6 @@ function Base.zero(A::GenericSparseMatrixCSR)
     return GenericSparseMatrixCSR(A.m, A.n, rowptr, rowval, nzval)
 end
 
-function Base.:(*)(α::Number, A::GenericSparseMatrixCSR)
-    return GenericSparseMatrixCSR(
-        A.m,
-        A.n,
-        copy(getrowptr(A)),
-        copy(colvals(A)),
-        α .* nonzeros(A),
-    )
-end
-Base.:(*)(A::GenericSparseMatrixCSR, α::Number) = α * A
-Base.:(/)(A::GenericSparseMatrixCSR, α::Number) = (1 / α) * A
-
 function Base.:-(A::GenericSparseMatrixCSR)
     return GenericSparseMatrixCSR(A.m, A.n, copy(A.rowptr), copy(A.colval), -A.nzval)
 end
@@ -363,8 +351,7 @@ function Base.:+(A::GenericSparseMatrixCSR, B::GenericSparseMatrixCSR)
     )
 
     C = GenericSparseMatrixCSR(m, n, rowptr_C, colval_C, nzval_C)
-    dropzeros!(C)
-    return C
+    return dropzeros(C)
 end
 
 # Addition with transpose/adjoint support
@@ -657,6 +644,13 @@ function SparseArrays.dropzeros!(A::GenericSparseMatrixCSR)
     cumsum_nnz = _cumsum_AK(nnz_per_row)
     total_nnz = @allowscalar cumsum_nnz[end]
 
+    if total_nnz == 0
+        # All elements are zeros - some GPU backends (e.g., Metal) don't support
+        # resize to 0. Keep the stored zeros; users can use dropzeros() (non-mutating)
+        # which returns a new matrix with properly empty arrays.
+        return A
+    end
+
     # Allocate temporary arrays for new data
     new_rowptr = similar(getrowptr(A))
     new_colval = similar(colvals(A), total_nnz)