rowstart for PlusOp/TimesOp for InfiniteCardinal (#500)

Author: jishnub

Project.toml

@@ -1,6 +1,6 @@
 name = "ApproxFunBase"
 uuid = "fbd15aa5-315a-5a7d-a8a4-24992e37be05"
-version = "0.8.40"
+version = "0.8.41"
 
 [deps]
 AbstractFFTs = "621f4979-c628-5d54-868e-fcf4e3e8185c"

src/Operators/general/algebra.jl

@@ -48,6 +48,7 @@ for (OP, mn) in ((:colstart, :min), (:colstop, :max), (:rowstart, :min), (:rowst
             mapreduce(op -> $OP(op, k), $mn, P.ops)
         end
     end
+    @eval $OP(::PlusOperator, ::InfiniteCardinal{0}) = ℵ₀
 end
 
 # We assume that a Vector{Operator{T}} occurs when incompatible operators are added
@@ -340,10 +341,10 @@ else
     promotetimes(args...) = _promotetimes(args...)
 end
 @inline function _promotetimes(opsin,
-    dsp=domainspace(last(opsin)),
-    anytimesop=true)
+        dsp=domainspace(last(opsin)),
+        anytimesop=true)
 
-    @assert length(opsin) > 1 "need at least 2 operators"
+    length(opsin) > 1 || throw(ArgumentError("need at least 2 operators"))
     ops, bw, bbw, sbbw, ibbb, irb = __promotetimes(opsin, dsp, anytimesop)
     sz = _timessize(ops)
     isaf = sz[1] == 1 && isconstspace(rangespace(first(ops)))
@@ -356,14 +357,12 @@ function __promotetimes(opsin, dsp, anytimesop)
 
     for k in reverse(eachindex(opsin))
         op = opsin[k]
-        if !isa(op, Conversion)
-            op_dsp = promotedomainspace(op, dsp)
-            dsp = rangespace(op_dsp)
-            if anytimesop && isa(op_dsp, TimesOperator)
-                append!(ops, view(op_dsp.ops, reverse(axes(op_dsp.ops, 1))))
-            else
-                push!(ops, op_dsp)
-            end
+        op_dsp = promotedomainspace(op, dsp)
+        dsp = rangespace(op_dsp)
+        if anytimesop && isa(op_dsp, TimesOperator)
+            append!(ops, view(op_dsp.ops, reverse(axes(op_dsp.ops, 1))))
+        else
+            push!(ops, op_dsp)
         end
     end
     reverse!(ops), bandwidthssum(bandwidths, ops), bandwidthssum(blockbandwidths, ops),
@@ -433,6 +432,7 @@ for OP in (:rowstart, :rowstop)
         end
         k
     end
+    @eval $OP(::TimesOperator, ::InfiniteCardinal{0}) = ℵ₀
 end
 
 for OP in (:colstart, :colstop)

test/PolynomialSpacesTests.jl

@@ -305,6 +305,13 @@ Base.:(==)(a::UniqueInterval, b::UniqueInterval) = (@assert a.parentinterval ==
         @testset for I in CartesianIndices(B)
             @test B[I] ≈ P[Tuple(I)...] rtol=1e-8 atol=eps(eltype(B))
         end
+
+        D1 = Derivative(Chebyshev())
+        P1 = PartialInverseOperator(Conversion(domainspace(D1), rangespace(D1)))
+        D2 = Derivative(Chebyshev(), 2)
+        P2 = PartialInverseOperator(Conversion(domainspace(D2), rangespace(D2)))
+        @test (P1 * D1)[1:10, 1:10] ≈ (P2 * D1)[1:10, 1:10]
+        @test ((P1 * D1)^2)[1:10, 1:10] ≈ (P2 * D2)[1:10, 1:10]
     end
 
     @testset "istriu/istril" begin
@@ -378,6 +385,12 @@ Base.:(==)(a::UniqueInterval, b::UniqueInterval) = (@assert a.parentinterval ==
         x = Fun()
         A = @inferred Derivative() * Multiplication(x, Chebyshev())
         @test A * x ≈ 2x
+        @test ApproxFunBase.rowstart(A, ApproxFunBase.ℵ₀) == ApproxFunBase.ℵ₀
+    end
+
+    @testset "PlusOperator" begin
+        A = Derivative(Chebyshev()) + Derivative(Chebyshev())
+        @test ApproxFunBase.rowstart(A, ApproxFunBase.ℵ₀) == ApproxFunBase.ℵ₀
     end
 
     @testset "ConstantSpace" begin