Trac #31479: Do not use pynac's poly_mul_expand function until it has…

… been debugged

Pynac's `poly_mul_expand` function silently produces wrong results when
expanding certain sums. This ticket eliminates its use by pynac's
`ex::expand` method, and therefore provides a (temporary) fix for the
problems reported in #31077 and #31411.

This is part of metaticket #31478.

Use of the `poly_mul_expand` function can be re-enabled after the bugs
have been fixed.

URL: https://trac.sagemath.org/31479
Reported by: gh-DaveWitteMorris
Ticket author(s): Dave Morris
Reviewer(s): Volker Braun, Matthias Koeppe

build/pkgs/configure/checksums.ini

@@ -1,4 +1,4 @@
 tarball=configure-VERSION.tar.gz
-sha1=8809623aaeee9f8b0c9de1de8309e873d4f6d9cc
-md5=11323b5d74baef36ddb0012a83c2e867
-cksum=1815530444
+sha1=947060891418045c7a06d165b29fbf8486f99fe2
+md5=bc468c0b6934cd87f5a9ec3560adff24
+cksum=124663050

build/pkgs/configure/package-version.txt

@@ -1 +1 @@
-034759c8ef41f10a5f4d0925c1fe2cee1ae69ea1
+df398dd79db1994aa00b43108b6f7261ecba055b

build/pkgs/pynac/package-version.txt

@@ -1 +1 @@
-0.7.27.p3
+0.7.27.p4

build/pkgs/pynac/patches/handle_factor.patch

@@ -0,0 +1,43 @@
+diff --git a/ginac/expairseq.cpp b/ginac/expairseq.cpp
+index dd87d18..556b713 100644
+--- a/ginac/expairseq.cpp
++++ b/ginac/expairseq.cpp
+@@ -1032,7 +1032,12 @@ void expairseq::make_flat(const epvector &v, bool do_index_renaming)
+
+ 		if (ex_to<basic>(elem.rest).tinfo()==this->tinfo() &&
+ 		    this->can_make_flat(elem)) {
+-			ex newrest = mf.handle_factor(elem.rest, elem.coeff);
++		        ex newrest;
++		        if (is_exactly_a<numeric>(elem.coeff) and elem.coeff.is_zero()) {
++		            newrest = default_overall_coeff();
++		        } else {
++		            newrest = elem.rest;
++		        }
+ 			const expairseq &subseqref = ex_to<expairseq>(newrest);
+ 			combine_overall_coeff(subseqref.overall_coeff,
+ 			                      ex_to<numeric>(elem.coeff));
+@@ -1043,15 +1048,15 @@ void expairseq::make_flat(const epvector &v, bool do_index_renaming)
+ 			if (elem.is_canonical_numeric())
+ 				combine_overall_coeff(ex_to<numeric>(mf.handle_factor(elem.rest, _ex1)));
+ 			else {
+-				const ex& rest = elem.rest;
+-				const ex& newrest = mf.handle_factor(rest, elem.coeff);
+-                                if (newrest.is_zero())
+-                                        combine_overall_coeff(*_num0_p);
+-				else if (are_ex_trivially_equal(newrest, rest))
+-					seq.push_back(elem);
+-				else
+-					seq.emplace_back(newrest, elem.coeff);
+-			}
++			        if ((is_exactly_a<numeric>(elem.coeff) and elem.coeff.is_zero())
++			                or (is_exactly_a<numeric>(elem.rest)
++			                    and (ex_to<numeric>(elem.rest).is_equal(default_overall_coeff())))) {
++			            combine_overall_coeff(default_overall_coeff());
++			        }
++			        else {
++			                seq.push_back(elem);
++			        }
++			    }
+ 		}
+ 	}
+ }

src/sage/symbolic/expression.pyx

@@ -5490,11 +5490,19 @@ cdef class Expression(CommutativeRingElement):
             sage: integrate(f(x), x, 0, a).subs(a=cos(a))
             integrate(f(x), x, 0, cos(a))
 
+        Check that :trac:`31554` is fixed::
+
+            sage: a,b,c,d,x,y = var("a b c d x y")
+            sage: with hold:
+            ....:     print((2*x^0*a + b*y^1).subs({x:c, y:c*d}))
+            b*c*d + 2*a
+
         Check that :trac:`31530` is fixed::
 
             sage: a, b = var("a b")
             sage: (a + b*x).series(x, 2).subs(a=a, b=b)
             (a) + (b)*x + Order(x^2)
+
         """
         cdef dict sdict = {}
         cdef GEx res