From 01dbcfb0352ad6ff9d46c723c2aa59352a57b251 Mon Sep 17 00:00:00 2001
From: Diogo Cordeiro <diogo@fc.up.pt>
Date: Sun, 25 Nov 2018 17:50:49 +0000
Subject: [PATCH] Let scale polynomial support negatives

---
 polymani.pl | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/polymani.pl b/polymani.pl
index 42c4699..04d1a0c 100644
--- a/polymani.pl
+++ b/polymani.pl
@@ -662,7 +662,6 @@ term_to_canon(L, [N | L2]) :-
 %
 term_to_canon_with_coefficient(N, [N2 | TS], TS2) :-
     number(N2),
-    %% {N2 >= 0; N2 < 0},
     term_to_canon_with_coefficient(N3, TS, TS2),
     N is N2 * N3,
     !.
@@ -732,7 +731,7 @@ add_terms([NL | TL], [NR | TR], [N2 | TL2]) :-
     %% have a number in front, so it can be added
     term_to_canon([NL | TL], [NL2 | TL2]),
     term_to_canon([NR | TR], [NR2 | TR2]),
-    %% If they rest of the term is the same
+    %% If the rest of the term is the same
     TL2 == TR2,
     %% Add the coeficients
     N2 is NL2 + NR2.
@@ -856,13 +855,16 @@ scale_polynomial(P, C, S) :-
     polynomial_to_list(P, L),
     %% Convert each term to a list
     maplist(term_to_list, L, L2),
+    %% Canonize terms
+    maplist(term_to_canon, L2, L3),
     %% Append C to the start of each sublist
-    maplist(cons(C), L2, L3),
-    %% Convert back
-    maplist(term_to_list, L4, L3),
+    maplist(cons(C), L3, L4),
+    %% Convert to a list of terms
+    maplist(term_to_list, L5, L4),
     %% Simplify the resulting polynomial
-    simplify_polynomial_as_list(L4, L5),
-    list_to_polynomial(L5, S),
+    simplify_polynomial_as_list(L5, L6),
+    %% Return as a simplified polynomial
+    list_to_polynomial(L6, S),
     !.
 %% Tests:
 %% ?- scale_polynomial(3*x^2, 2, S).
@@ -874,7 +876,7 @@ scale_polynomial(P, C, S) :-
 %
 cons(C, L, [C | L]).
 %% Tests:
-%% It just trivially works.
+%% No need for tests as it is trivially correct.
 
 %% add_polynomial(+P1:polynomial,+P2:polynomial,-S:polynomial) is det
 %