Backport isconstant (#637)

Author: jishnub

src/Fun.jl

@@ -107,7 +107,8 @@ julia> coefficients(f, Legendre()) ≈ [0, 0, 1]
 true
 ```
 """
-function coefficients(f::Fun,msp::Space)
+coefficients(f::Fun,msp::Space) = _coefficients(f::Fun,msp::Space)
+function _coefficients(f::Fun,msp::Space)
     #zero can always be converted
     fc = f.coefficients
     if ncoefficients(f) == 0 || (ncoefficients(f) == 1 && fc[1] == 0)
@@ -777,9 +778,10 @@ isapprox(g::Number, f::Fun; kw...) = isapprox(g*ones(space(f)), f; kw...)
 isreal(f::Fun{<:RealSpace,<:Real}) = true
 isreal(f::Fun) = false
 
-iszero(f::Fun)    = all(iszero,f.coefficients)
-
+iszero(f::Fun)    = all(iszero, coefficients(f)) || all(iszero, values(f))
 
+# Deliberately not named isconst or isconstant to avoid conflicts with Base or DomainSets
+isconstantfun(f::Fun) = iszero(f - first(f))
 
 # sum, integrate, and idfferentiate are in CalculusOperator
 

src/Operators/Operator.jl

@@ -197,7 +197,7 @@ opissymmetric(::OperatorStyle, A) = false
 for f in [:domainspace, :rangespace]
     opf = Symbol(:op, f)
     @eval begin
-        $opf(::OperatorStyle, A) = error("Override domainspace for $(typeof(A))")
+        $opf(::OperatorStyle, A) = error("Override $($f) for $(typeof(A))")
         $opf(S::StyleConflict, A) = $opf(dominantstyle(S, $f, A), A)
     end
 end

src/Spaces/ConstantSpace.jl

@@ -81,7 +81,8 @@ ones(S::Union{AnyDomain,UnsetSpace}) = ones(ConstantSpace())
 zeros(S::AnyDomain) = zero(ConstantSpace())
 zero(S::UnsetSpace) = zero(ConstantSpace())
 _first_or_zero(f::AbstractVector) = get(f, 1, zero(eltype(f)))
-function evaluate(f::AbstractVector,::ConstantSpace,x...)
+function evaluate(f::AbstractVector, sp::ConstantSpace, x)
+    x in domain(sp) || return zero(eltype(f))
     _first_or_zero(f)
 end
 evaluate(f::AbstractVector,::ZeroSpace,x...)=zero(eltype(f))
@@ -143,6 +144,10 @@ function getindex(C::ConcreteConversion{CS,S,T},k::Integer,j::Integer) where {CS
     k ≤ ncoefficients(on) ? strictconvert(T,on.coefficients[k]) : zero(T)
 end
 
+function coefficients(f::Fun, msp::ConstantSpace)
+    isconstantfun(f) || throw(ArgumentError("cannot convert a non-constant Fun to ConstantSpace"))
+    _coefficients(f, msp)
+end
 
 coefficients(f::AbstractVector,sp::ConstantSpace{Segment{SVector{2,TT}}},
              ts::TensorSpace{SV,DD}) where {TT,SV,DD<:EuclideanDomain{2}} =
@@ -155,6 +160,9 @@ coefficients(f::AbstractVector, sp::ConstantSpace{<:Domain{<:Number}}, ts::Space
 coefficients(f::AbstractVector, sp::ConstantSpace, ts::Space) =
     f[1]*ones(ts).coefficients
 
+# a Fun{<:ConstantSpace} corresponds to a constant value within the domain, irrespective of the domain
+first(f::Fun{<:ConstantSpace}) = convert(Number, f)
+last(f::Fun{<:ConstantSpace}) = convert(Number, f)
 
 ########
 # Evaluation

src/Spaces/DiracSpace.jl

@@ -79,19 +79,20 @@ Fun(::typeof(identity), S::DiracSpace) = Fun(PointSpace(S.points),S.points)
 transform(S::PointSpace,v::AbstractVector,plan...) = v
 values(f::Fun{S}) where S<:PointSpace = coefficient(f,:)
 
-function evaluate(f::AbstractVector,PS::PointSpace,x::Number)
-    p = findfirst(y->isapprox(x,y),PS.points)
+first(f::Fun{<:PointSpace}) = coefficients(f)[1]
+last(f::Fun{<:PointSpace}) = coefficients(f)[end]
+
+function evaluate(f::AbstractVector, PS::PointSpace, x)
+    p = findfirst(≈(convert(Number,x)), PS.points)
     if p === nothing
         zero(eltype(f))
     else
         f[p]
     end
 end
 
-function evaluate(f::AbstractVector, PS::DiracSpace, x::Number)
-    x ∉ domain(PS) && return zero(eltype(f))
-
-    p = findfirst(y->isapprox(x,y), PS.points)
+function evaluate(f::AbstractVector, PS::DiracSpace, x)
+    p = findfirst(≈(convert(Number,x)), PS.points)
     if p === nothing
         zero(eltype(f))
     else
@@ -100,7 +101,7 @@ function evaluate(f::AbstractVector, PS::DiracSpace, x::Number)
 end
 
 Base.sum(f::Fun{DS}) where DS<:DiracSpace =
-    sum(f.coefficients[1:dimension(space(f))])
+    sum(@view f.coefficients[1:dimension(space(f))])
 
 DiracDelta(x::Number)=Fun(DiracSpace(x),[1.])
 DiracDelta()=DiracDelta(0.)

test/SpacesTest.jl

@@ -1,16 +1,20 @@
 using ApproxFunBase
-using Test
 using ApproxFunBase: PointSpace, HeavisideSpace, PiecewiseSegment, dimension, SVector, checkpoints, AnyDomain
-using StaticArrays
 using BandedMatrices: rowrange, colrange, BandedMatrix
+using DomainSets: Point
 using LinearAlgebra
+using StaticArrays
+using Test
 
 @testset "Spaces" begin
     @testset "PointSpace" begin
         @test eltype(domain(PointSpace([0,0.1,1])) ) == Float64
 
         f = @inferred Fun(x->(x-0.1),PointSpace([0,0.1,1]))
         @test roots(f) == [0.1]
+        @test first(f) == -0.1
+        @test last(f) == 0.9
+        @test f(Point(0)) == -0.1
 
         a = @inferred Fun(exp, space(f))
         @test f/a == @inferred Fun(x->(x-0.1)*exp(-x),space(f))
@@ -204,6 +208,11 @@ using LinearAlgebra
             F = Fun{typeof(PointSpace(1:3)), Float32}
             @test ApproxFunBase.cfstype(F) == Float32
         end
+
+        @testset "isconstantfun" begin
+            f = Fun(PointSpace(1:4), ones(4))
+            @test ApproxFunBase.isconstantfun(f)
+        end
     end
 
     @testset "DiracSpace" begin
@@ -212,6 +221,8 @@ using LinearAlgebra
         @test f(0.5) == 0
         @test f(5) == 0
         @test isinf(f(0))
+        @test isinf(f(Point(0)))
+        @test sum(f) == 6
     end
 
     @testset "Derivative operator for HeavisideSpace" begin
@@ -317,6 +328,12 @@ using LinearAlgebra
         @test g >= f
         @test 1 < f < 3
         @test differentiate(f) == Fun(0, ConstantSpace(0..1))
+        @test f(-1) == 0
+        @test first(f) == last(f) == 2
+        @test ApproxFunBase.isconstantfun(f)
+
+        f = Fun(2, ConstantSpace())
+        @test first(f) == last(f) == 2
 
         @test maxspace(ConstantSpace(Point(1)), ConstantSpace(Point(2))) == ConstantSpace(Point(1) ∪ Point(2))
         @test maxspace(ConstantSpace(Point(1)), ConstantSpace(AnyDomain())) == ConstantSpace(Point(1))

test/runtests.jl

@@ -795,3 +795,10 @@ include("show.jl")
 
     @test @inferred(chebyshev_clenshaw(BigInt[1], 1)) == 1
 end
+
+@testset "Unimplemented functionality errors" begin
+    struct MyOperator{T} <: ApproxFunBase.Operator{T} end
+    X = MyOperator{Float64}();
+    @test_throws ErrorException("Override domainspace for $(typeof(X))") domainspace(X)
+    @test_throws ErrorException("Override rangespace for $(typeof(X))") rangespace(X)
+end