Implement calculus operations for ConstantSpace (#595)

* Implement calculus operations for ConstantSpace

* Add test for integrate() on ConstantSpace

* Infer domain space in integrate

* Revert "Add test for integrate() on ConstantSpace"

This reverts commit 0a1269a.

* Add test for differentiate()

* Version bump to v0.9.15

Author: LucasAschenbach

Project.toml

@@ -1,6 +1,6 @@
 name = "ApproxFunBase"
 uuid = "fbd15aa5-315a-5a7d-a8a4-24992e37be05"
-version = "0.9.14"
+version = "0.9.15"
 
 [deps]
 AbstractFFTs = "621f4979-c628-5d54-868e-fcf4e3e8185c"

src/Spaces/ConstantSpace.jl

@@ -254,7 +254,7 @@ choosedomainspace(M::ConcreteMultiplication{D,UnsetSpace},sp::Space) where {D<:C
 Base.isfinite(f::Fun{CS}) where {CS<:ConstantSpace} = isfinite(Number(f))
 
 
+## Calculus
 
-
-
-
+integrate(f::Fun{<:ConstantSpace{<:IntervalOrSegment}}) = Number(f) * Fun(domain(f))
+differentiate(f::Fun{<:ConstantSpace{<:IntervalOrSegment}}) = zero(f)

test/SpacesTest.jl

@@ -309,6 +309,7 @@ using LinearAlgebra
         @test g > f
         @test g >= f
         @test 1 < f < 3
+        @test differentiate(f) == Fun(0, ConstantSpace(0..1))
 
         @test maxspace(ConstantSpace(Point(1)), ConstantSpace(Point(2))) == ConstantSpace(Point(1) ∪ Point(2))
         @test maxspace(ConstantSpace(Point(1)), ConstantSpace(AnyDomain())) == ConstantSpace(Point(1))