Implement taking subbasis of subbasis (#99)

* Implement taking subbasis of subbasis

* Use sub_basis

* Remove debug

* Fix

Author: blegat

src/bases_fixed.jl

@@ -113,6 +113,36 @@ struct SubBasis{T,I,K,B<:AbstractBasis{T,K},V<:AbstractVector{K}} <:
     end
 end
 
+"""
+    sub_basis(basis::SubBasis, indices::Vector)
+
+Return a `SubBasis` of the same `parent` but the subset of keys
+`basis.keys[indices]`.
+"""
+function sub_basis(basis::SubBasis, indices::AbstractVector)
+    # If `basis.is_sorted` is `true` and `indices` is not sorted,
+    # maybe we should sort it automatically ?
+    # Or maybe it's best to just error so that the user has to sort it explicitly
+    @assert issorted(indices)
+    return SubBasis(parent(basis), basis.keys[indices])
+end
+
+"""
+    sub_basis(basis::ImplicitBasis, keys::AbstractVector)
+
+Return a `SubBasis` of `basis` but the subset of keys `keys`.
+
+## Note
+
+Even though the constructor `SubBasis(basis, keys)` allows `basis`
+to be a `ExplicitBasis`, this function restricts it to be
+an `ImplicitBasis` in order to provide an interface that would
+help catch common mistakes.
+"""
+function sub_basis(basis::ImplicitBasis, keys::AbstractVector)
+    return SubBasis(basis, keys)
+end
+
 Base.parent(sub::SubBasis) = sub.parent_basis
 
 function Base.:(==)(a::SubBasis, b::SubBasis)

test/basic.jl

@@ -46,12 +46,15 @@ Base.iterate(b::DummyBasis, args...) = iterate(b.elements, args...)
     @test A == StarAlgebra(1.0, SA.MappedBasis(b, float, error))
     @test A != StarAlgebra(1.0, m2)
 
-    sub = SA.SubBasis(m, Irrational[π])
+    sub = SA.sub_basis(m, Irrational[π])
     B = StarAlgebra(1.0, sub)
     @test B == B
-    @test B == StarAlgebra(1.0, SA.SubBasis(m, Irrational[π]))
-    @test B != StarAlgebra(1.0, SA.SubBasis(m, Irrational[ℯ]))
-    @test B != StarAlgebra(1.0, SA.SubBasis(m2, Irrational[π]))
+    @test B == StarAlgebra(1.0, SA.sub_basis(m, Irrational[π]))
+    @test B != StarAlgebra(1.0, SA.sub_basis(m, Irrational[ℯ]))
+    @test B != StarAlgebra(1.0, SA.sub_basis(m2, Irrational[π]))
+    @test B == StarAlgebra(1.0, SA.sub_basis(SA.sub_basis(m, Irrational[π, ℯ]), 1:1))
+    @test B != StarAlgebra(1.0, SA.sub_basis(SA.sub_basis(m, Irrational[π, ℯ]), 1:2))
+    @test B != StarAlgebra(1.0, SA.sub_basis(SA.sub_basis(m, Irrational[π, ℯ]), 2:2))
 
     el = SA.AlgebraElement(
         [Variable()],

test/graded_lex.jl

@@ -22,7 +22,7 @@ import StarAlgebras as SA
     @test c.coeffs.values == [4, -4, 12, 1, -6, 9]
     c_keys = [(0, 0), (0, 1), (1, 0), (0, 2), (1, 1), (2, 0)]
     @test c.coeffs.basis_elements == c_keys
-    sub = SA.SubBasis(SA.basis(alg), c_keys)
+    sub = SA.sub_basis(SA.basis(alg), c_keys)
     @test sub.is_sorted
     for (i, key) in enumerate(c_keys)
         el = SA.basis(alg)[key]

test/perm_grp_algebra.jl

@@ -124,7 +124,7 @@ import StarAlgebras as SA
         Random.seed!(0)
         S1 = unique!(rand(G, 7))
         S = unique!([S1; [a * b for a in S1 for b in S1]])
-        subb = SA.SubBasis(db, S)
+        subb = SA.sub_basis(db, S)
         a = S1[1]
         @test subb[a] == 1
         @test a in subb
@@ -160,7 +160,7 @@ import StarAlgebras as SA
         end
 
         S2 = unique([S; one(G)])
-        subb2 = SA.SubBasis(db, S2)
+        subb2 = SA.sub_basis(db, S2)
         let sRG = SA.StarAlgebra(G, subb2)
             x = let z = spzeros(Int, length(SA.basis(sRG)))
                 z[rand(1:length(S2), 10)] += rand(-1:1, 10)

test/quadratic_form.jl

@@ -82,7 +82,7 @@ end
     implicit = SA.MappedBasis(NaturalNumbers(), float, Int)
     @test 3.0 in implicit
     @test haskey(implicit, 3)
-    explicit = SA.SubBasis(implicit, 1:3)
+    explicit = SA.sub_basis(implicit, 1:3)
     @test 3.0 in explicit
     @test collect(explicit) == [1.0, 2.0, 3.0]
     @test haskey(explicit, 3)
@@ -109,7 +109,7 @@ end
     implicit = cheby_basis()
     mstr = ChebyMStruct(implicit)
     mt = SA.MTable(mstr, (0, 0))
-    sub = SA.SubBasis(implicit, 1:3)
+    sub = SA.sub_basis(implicit, 1:3)
     test_vector_interface(sub)
     fixed = SA.FixedBasis(implicit; n = 3)
     test_vector_interface(fixed)