add dot(x, A, y) for sparse matrices

docs/src/sparse/intro.md

@@ -211,6 +211,12 @@ Various products:
 *(::SRow{T}, ::SMat{T}) where {T}
 ```
 
+```@docs
+dot(::SRow{T}, ::SMat{T}, ::SRow{T}) where T
+dot(::MatrixElem{T}, ::SMat{T}, ::MatrixElem{T}) where T
+dot(::AbstractVector{T}, ::SMat{T}, ::AbstractVector{T}) where T
+```
+
 Other:
 ```@docs
 sparse(::SMat)

src/Sparse/Matrix.jl

@@ -723,6 +723,91 @@ function *(A::SMat, b)
   return A * base_ring(A)(b)
 end
 
+################################################################################
+#
+#  Dot product
+#
+################################################################################
+
+@doc raw"""
+    dot(x::SRow{T}, A::SMat{T}, y::SRow{T}) where T -> T
+
+Return the generalized dot product `dot(x, A*y)`.
+"""
+function dot(x::SRow{T}, A::SMat{T}, y::SRow{T}) where T
+  v = zero(T)
+  px = 1
+  for i in 1:length(A.rows)
+    while px <= length(x.pos) && x.pos[px] < i
+      px += 1
+    end
+    if px > length(x.pos)
+      break
+    elseif x.pos[px] > i
+      continue
+    end
+
+    s = zero(T)
+    py = 1
+    for j in 1:length(A[i].pos)
+      while py <= length(y.pos) && y.pos[py] < A[i].pos[j]
+        py += 1
+      end
+      if py > length(y.pos)
+        break
+      elseif y.pos[py] > A[i].pos[j]
+        continue
+      end
+
+      s += A[i].values[j] * y.values[py]
+    end
+
+    v += x.values[px] * s
+  end
+
+  return v
+end
+
+@doc raw"""
+    dot(x::AbstractVector{T}, A::SMat{T}, y::AbstractVector{T}) where T -> T
+
+Return the generalized dot product `dot(x, A*y)`.
+"""
+function dot(x::AbstractVector{T}, A::SMat{T}, y::AbstractVector{T}) where T
+  @req length(x) == nrows(A) && ncols(A) <= length(y) "incompatible matrix dimensions"
+
+  v = zero(T)
+  for i in 1:length(A.rows)
+    s = T(0)
+    for j in 1:length(A[i].pos)
+      s += A[i].values[j] * y[A[i].pos[j]]
+    end
+    v += x[i] * s
+  end
+
+  return v
+end
+
+@doc raw"""
+    dot(x::MatrixElem{T}, A::SMat{T}, y::MatrixElem{T}) where T -> T
+
+Return the generalized dot product `dot(x, A*y)`.
+"""
+function dot(x::MatrixElem{T}, A::SMat{T}, y::MatrixElem{T}) where T
+  @req length(x) == nrows(A) && ncols(A) <= length(y) "incompatible matrix dimensions"
+
+  v = zero(T)
+  for i in 1:length(A.rows)
+    s = zero(T)
+    for j in 1:length(A[i].pos)
+      s += A[i].values[j] * y[A[i].pos[j]]
+    end
+    v += x[i] * s
+  end
+
+  return v
+end
+
 ################################################################################
 #
 #  Submatrix

test/Sparse/Matrix.jl

@@ -207,6 +207,39 @@ using Hecke.SparseArrays
   E = @inferred D * R(3)
   @test E == sparse_matrix(R, [3 0 0; 0 0 3; 0 0 0])
 
+  # Dot product
+
+  D = sparse_matrix(ZZ, [4 -2; -2 2])
+  E = sparse_matrix(ZZ, [3 0 0; 0 3 0])
+
+  @test dot(sparse_row(ZZ, [1], [1]), D, sparse_row(ZZ, [1], [1])) == 4
+  @test dot(sparse_row(ZZ, [1, 2], [1, 1]), D, sparse_row(ZZ, [1, 2], [1, 2])) == 2
+  @test dot(sparse_row(ZZ, [1], [1]), D, sparse_row(ZZ, [2], [1])) == -2
+
+  @test dot(sparse_row(ZZ, [1, 4], [1, 2]), D, sparse_row(ZZ, [2], [1])) == -2
+  @test dot(sparse_row(ZZ, [1, 4], [1, 2]), E, sparse_row(ZZ, [2], [1])) == 0
+  @test dot(sparse_row(ZZ, [1, 2], [1, 2]), E, sparse_row(ZZ, [2], [1])) == 6
+
+  @test dot(ZZRingElem[1, 0], D, ZZRingElem[1, 0]) == 4
+  @test dot(ZZRingElem[1, 1], D, ZZRingElem[1, 2]) == 2
+  @test dot(ZZRingElem[1, 0], D, ZZRingElem[0, 1]) == -2
+  @test dot(ZZRingElem[1, 0], E, ZZRingElem[0, 1, 2]) == 0
+  @test dot(ZZRingElem[0, 1], E, ZZRingElem[0, 1, 2]) == 3
+
+  @test dot(ZZ[1 0], D, ZZ[1 0]) == 4
+  @test dot(ZZ[1; 1], D, ZZ[1 2]) == 2
+  @test dot(ZZ[1 0], D, ZZ[0; 1]) == -2
+  @test dot(ZZ[1 0], E, ZZ[0 1 2]) == 0
+  @test dot(ZZ[0 1], E, ZZ[0 1 2]) == 3
+
+  @test_throws ArgumentError dot(ZZRingElem[1], D, ZZRingElem[0, 1])
+  @test_throws ArgumentError dot(ZZRingElem[1, 0], D, ZZRingElem[0])
+  @test_throws ArgumentError dot(ZZRingElem[1, 0, 2], E, ZZRingElem[0, 1])
+
+  @test_throws ArgumentError dot(ZZ[1 0 0], D, ZZ[1 0])
+  @test_throws ArgumentError dot(ZZ[0 1 2], E, ZZ[0 1])
+  @test_throws ArgumentError dot(ZZ[1 0; 0 0], D, ZZ[1 0 0 0])
+
   # Submatrix
 
   D = sparse_matrix(FlintZZ, [1 5 3; 0 0 0; 0 1 0])