From 3dfb15ac19c88aec47f7f035131e4ce7aead570e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Beno=C3=AEt=20Legat?= <benoit.legat@gmail.com>
Date: Sat, 2 Oct 2021 11:36:16 -0400
Subject: [PATCH] Drop variables not in any substitution (#95)

---
 src/subs.jl      | 2 +-
 src/var.jl       | 5 +++++
 test/runtests.jl | 6 +++++-
 3 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/src/subs.jl b/src/subs.jl
index 8004192..51c0bb9 100644
--- a/src/subs.jl
+++ b/src/subs.jl
@@ -94,7 +94,7 @@ function _subs(::MP.Eval, p::Polynomial{C, T}, vals::AbstractVector{S}) where {C
 end
 function _subs(::MP.Subs, p::Polynomial{C, T}, vals::AbstractVector{S}) where {C, T, S}
     Tout = MA.promote_operation(*, T, MP.coefficienttype(S))
-    q = zero_with_variables(Polynomial{C, Tout}, variables(p))
+    q = zero_with_variables(Polynomial{C, Tout}, mergevars_of(PolyVar{C}, vals)[1])
     for i in 1:length(p.a)
         MA.mutable_operate!(+, q, p.a[i] * monoeval(p.x.Z[i], vals))
     end
diff --git a/src/var.jl b/src/var.jl
index 947ec14..0f66f8f 100644
--- a/src/var.jl
+++ b/src/var.jl
@@ -104,3 +104,8 @@ function mergevars(varsvec::Vector{Vector{PV}}) where {PV<:PolyVar}
     maps = mergevars_to!(vars, varsvec)
     return vars, maps
 end
+function mergevars_of(::Type{PolyVar{C}}, polys::AbstractVector) where {C}
+    varsvec = Vector{PolyVar{C}}[variables(p) for p in polys if p isa PolyType]
+    # TODO avoid computing `maps`
+    return mergevars(varsvec)
+end
diff --git a/test/runtests.jl b/test/runtests.jl
index 47b75dd..25d532b 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -16,7 +16,7 @@ end
     @polyvar x[1:2]
     p1 = x[1] * 0.0 + x[2] * 0
     p2 = ( x[1] + x[2] ) * 0.0
-    @test variables(p1) == x 
+    @test variables(p1) == x
     @test variables(p1) == variables(p2)
 
     @polyvar χ[1:4]
@@ -33,6 +33,10 @@ end
     # This is for Issue #92
     p3 = subs(p1, x => x)
     @test variables(p3) == x
+
+    p4 = x[1] + x[2]
+    @test variables(subs(p4, x[2] => 1)) == [x[1]]
+    @test variables(subs(p4, x[1] => 1)) == [x[2]]
 end
 
 include("mono.jl")