fix A default value when not provided in the constructor (#112)

* fix A default value when not provided in the constructor

* tests default A value

Author: geoffroyleconte

src/qpmodel.jl

@@ -148,10 +148,14 @@ function QuadraticModel(
   )
 end
 
+similar_empty_matrix(H::AbstractMatrix{T}, n::Integer) where {T} = similar(H, 0, n)
+similar_empty_matrix(::SparseMatrixCOO{T, I}, n::Integer) where {T, I} = SparseMatrixCOO(0, n, I[], I[], T[])
+similar_empty_matrix(::AbstractLinearOperator{T}, n::Integer) where {T} = opZeros(T, 0, n)
+
 function QuadraticModel(
   c::S,
   H::Union{AbstractMatrix{T}, AbstractLinearOperator{T}};
-  A::Union{AbstractMatrix, AbstractLinearOperator} = similar(c, 0, length(c)),
+  A::Union{AbstractMatrix, AbstractLinearOperator} = similar_empty_matrix(H, length(c)),
   lcon::S = S(undef, 0),
   ucon::S = S(undef, 0),
   lvar::S = fill!(S(undef, length(c)), T(-Inf)),

test/runtests.jl

@@ -207,6 +207,26 @@ end
   @test jtprod(SMLO, x, y) ≈ jtprod(SM, x, y)
   @test objgrad(SMLO, x)[1] ≈ objgrad(SM, x)[1]
   @test objgrad(SMLO, x)[2] ≈ objgrad(SM, x)[2]
+
+  # tests default A value
+  qp = QuadraticModel(
+    c,
+    SparseMatrixCOO(H.data),
+    lvar = lvar,
+    uvar = uvar,
+    c0 = 0.0,
+    name = "QM",
+  )
+  qpLO = QuadraticModel(
+    c,
+    LinearOperator(H),
+    lvar = lvar,
+    uvar = uvar,
+    c0 = 0.0,
+    name = "QMLO",
+  )
+  @test qp.data.A isa SparseMatrixCOO
+  @test qpLO.data.A isa AbstractLinearOperator
 end
 
 @testset "struct and coord CSC" begin