Use proper morphisms in primary decomposition helpers (oscar-system#3109

)
JohnAAbbott · Dec 21, 2023 · 25af855 · 25af855
1 parent 641f520
commit 25af855
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Showing 2 changed files with 15 additions and 10 deletions.
diff --git a/src/Rings/MPolyMap/MPolyAnyMap.jl b/src/Rings/MPolyMap/MPolyAnyMap.jl
@@ -276,6 +276,17 @@ function compose(F::MPolyAnyMap{D, C, <: Map, <: Any}, G::S) where {D, C, S <: M
   end
 end
 
+function compose(F::MPolyAnyMap{D, C, <: Map, <: Any}, G::S) where {D, C, S <: Generic.IdentityMap{C}}
+  @req codomain(F) === domain(G) "Incompatible (co)domain in composition"
+  f = coefficient_map(F)
+  if typeof(codomain(f)) === C
+    newcoeffmap = compose(f, G)
+    return hom(domain(F), codomain(G), newcoeffmap, G.(_images(F)), check=false)
+  else
+    return Generic.CompositeMap(F, G)
+  end
+end
+
 ################################################################################
 #
 #  Types computers

diff --git a/src/Rings/primary_decomposition_helpers.jl b/src/Rings/primary_decomposition_helpers.jl
@@ -34,11 +34,8 @@ function _expand_coefficient_field(R::MPolyRing{T}; rec_depth=0) where {T<:Union
   f = defining_polynomial(K)
   d = degree(f)
   powers = elem_type(P)[theta^k for k in 0:d-1]
-  function help_map(a)
-    return sum(c*powers[i] for (i, c) in enumerate(coefficients(a)); init=zero(P))
-  end
   R_flat, pr = quo(P, ideal(P, evaluate(f, theta)))
-  to_R_flat = hom(R, R_flat, x->pr(help_map(x)), gens(R_flat)[2:end])
+  to_R_flat = hom(R, R_flat, hom(K, R_flat, pr(theta)), gens(R_flat)[2:end])
   to_R = hom(R_flat, R, vcat([R(alpha)], gens(R)))
   return R_flat, to_R, to_R_flat
 end
@@ -55,7 +52,7 @@ function _expand_coefficient_field(
   f = defining_polynomials(K)
   d = degree.(f)
   R_flat, pr = quo(P, ideal(P, [evaluate(a, b) for (a, b) in zip(f, theta)]))
-  to_R_flat = hom(R, R_flat, x->evaluate(x.data, theta), gens(R_flat)[r+1:end])
+  to_R_flat = hom(R, R_flat, hom(K, R_flat, pr.(theta)), gens(R_flat)[r+1:end])
   to_R = hom(R_flat, R, vcat(R.(alpha), gens(R)))
   return R_flat, to_R, to_R_flat
 end
@@ -71,7 +68,7 @@ function _expand_coefficient_field(
   theta = gens(A_exp)[1:r]
   alpha = gens(coefficient_ring(A))
   to_A = hom(A_exp, A, vcat(A.(alpha), gens(A)))
-  to_A_exp = hom(A, A_exp, x->evaluate(x.data, theta), gens(A_exp)[r+1:end])
+  to_A_exp = hom(A, A_exp, hom(coefficient_ring(A), A_exp, theta), gens(A_exp)[r+1:end])
   return A_exp, to_A, to_A_exp
 end
 
@@ -109,10 +106,7 @@ function _expand_coefficient_field(Q::MPolyQuoRing{<:MPolyRingElem{T}}; rec_dept
   f = defining_polynomial(coefficient_ring(Q))
   d = degree(f)
   powers = [theta^k for k in 0:d-1]
-  function help_map(a)
-    return sum(c*powers[i] for (i, c) in enumerate(coefficients(a)); init=zero(Q_flat))
-  end
-  to_Q_flat = hom(Q, Q_flat, help_map, gens(Q_flat)[2:end])
+  to_Q_flat = hom(Q, Q_flat, hom(coefficient_ring(Q), Q_flat, theta), gens(Q_flat)[2:end])
   return Q_flat, to_Q, to_Q_flat
 end