From 016e801f80c38faeee453a5c3bf987a93e36c9d6 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Lars=20G=C3=B6ttgens?= <lars.goettgens@rwth-aachen.de>
Date: Tue, 8 Oct 2024 10:21:26 +0200
Subject: [PATCH] Add `zero!`, `one!`, `neg!` for MPoly

---
 src/generic/MPoly.jl                        | 42 ++++++++++++++++++---
 test/Rings-conformance-tests.jl             | 12 ++++++
 test/generic/FreeAssociativeAlgebra-test.jl |  4 +-
 test/generic/MPoly-test.jl                  | 15 ++++++++
 4 files changed, 66 insertions(+), 7 deletions(-)

diff --git a/src/generic/MPoly.jl b/src/generic/MPoly.jl
index 0a4d93e5b..96861478b 100644
--- a/src/generic/MPoly.jl
+++ b/src/generic/MPoly.jl
@@ -3886,6 +3886,43 @@ end
 #
 ###############################################################################
 
+function zero!(a::MPoly{T}) where {T <: RingElement}
+   a.length = 0
+   return a
+end
+
+function one!(a::MPoly{T}) where {T <: RingElement}
+   a.length = 1
+   fit!(a, 1)
+   a.coeffs[1] = one(base_ring(a))
+   a.exps = zero(a.exps)
+   return a
+end
+
+function neg!(a::MPoly{T}) where {T <: RingElement}
+   for i in 1:length(a)
+      a.coeffs[i] = neg!(a.coeffs[i])
+   end
+   return a
+end
+
+function neg!(z::MPoly{T}, a::MPoly{T}) where {T <: RingElement}
+   if z === a
+      return neg!(a)
+   end
+   z.length = length(a)
+   fit!(z, length(a))
+   for i in 1:length(a)
+      if isassigned(z.coeffs, i)
+         z.coeffs[i] = neg!(z.coeffs[i], a.coeffs[i])
+      else
+         z.coeffs[i] = -a.coeffs[i]
+      end
+   end
+   z.exps[:,1:length(a)] .= a.exps[:,1:length(a)]
+   return z
+end
+
 function add!(a::MPoly{T}, b::MPoly{T}, c::MPoly{T}) where {T <: RingElement}
    t = b + c
    a.coeffs = t.coeffs
@@ -3933,11 +3970,6 @@ function fit!(a::MPoly{T}, n::Int) where {T <: RingElement}
    end
    return nothing
 end
-#
-function zero!(a::MPoly{T}) where {T <: RingElement}
-   a.length = 0
-   return a
-end
 
 @doc raw"""
     setcoeff!(a::MPoly{T}, i::Int, c::T) where T <: RingElement
diff --git a/test/Rings-conformance-tests.jl b/test/Rings-conformance-tests.jl
index 8a97e7b28..442fbe839 100644
--- a/test/Rings-conformance-tests.jl
+++ b/test/Rings-conformance-tests.jl
@@ -42,6 +42,18 @@ function test_elem(Rx::AbstractAlgebra.PolyRing)
    return Rx(elem_type(R)[test_elem(R) for i in 1:rand(0:6)])
 end
 
+function test_elem(Rx::AbstractAlgebra.MPolyRing)
+   R = base_ring(Rx)
+   num_gens = ngens(Rx)
+   iszero(num_gens) && return Rx(test_elem(R))
+   len_bound = 8
+   exp_bound = rand(1:5)
+   len = rand(0:len_bound)
+   coeffs = [test_elem(R) for _ in 1:len]
+   exps = [[rand(0:exp_bound) for _ in 1:num_gens] for _ in 1:len]
+   return Rx(coeffs, exps)
+end
+
 function test_elem(S::Union{AbstractAlgebra.MatSpace,
                             AbstractAlgebra.MatRing})
    R = base_ring(S)
diff --git a/test/generic/FreeAssociativeAlgebra-test.jl b/test/generic/FreeAssociativeAlgebra-test.jl
index 31fcec114..5ee356686 100644
--- a/test/generic/FreeAssociativeAlgebra-test.jl
+++ b/test/generic/FreeAssociativeAlgebra-test.jl
@@ -220,8 +220,8 @@ end
    S, = free_associative_algebra(ZZ, 3)
    test_NCRing_interface(S)
 
-   R, x = QQ[:x]
-   S, = free_associative_algebra(R, 3)
+   R, = QQ[:x, :y]
+   S, = free_associative_algebra(R, :z => 1:3)
    test_NCRing_interface(S)
 end
 
diff --git a/test/generic/MPoly-test.jl b/test/generic/MPoly-test.jl
index 961ba2312..16045227a 100644
--- a/test/generic/MPoly-test.jl
+++ b/test/generic/MPoly-test.jl
@@ -1704,3 +1704,18 @@ end
    @test leading_coefficient(f, 1) == coefficients(f, 1)[end]
    @test content(f, 1) == y
 end
+
+@testset "Generic.MPoly.Ring_interface" begin
+  S, = polynomial_ring(QQ, 0)
+  test_Ring_interface_recursive(S)
+
+  S, = polynomial_ring(QQ, 1)
+  test_Ring_interface_recursive(S)
+
+  S, = polynomial_ring(ZZ, 2)
+  test_Ring_interface_recursive(S)
+
+  R, = QQ[:x]
+  S, = polynomial_ring(R, :z => 1:3)
+  test_Ring_interface(S) # _recursive needs too many ressources
+end