[Maxima-commits] [git] Maxima CAS branch master updated. branch-5_49-base-542-gcaa920e72

[tomasriker <tom...@us...>]

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- Log -----------------------------------------------------------------
commit caa920e729bb170e62c04b7a96fa714aabe92715
Author: David Scherfgen <d.s...@go...>
Date:   Wed May 27 22:12:35 2026 +0200

    Make FACTOR check that minimal polynomial is irreducible
    
    factor(a^2*g+a*g-a^2, g^3-1) -> division by zero, because g^3-1 = (g-1)*(g^2+g+1).
    
    This fixes bug #4658.

diff --git a/src/rat3e.lisp b/src/rat3e.lisp
index bf8b5f080..827d10c48 100644
--- a/src/rat3e.lisp
+++ b/src/rat3e.lisp
@@ -266,8 +266,14 @@
 		(setq minpoly* (cadr (ratrep* *alpha*)))
 		(when (or (pcoefp minpoly*)
 			  (not (univar (cdr minpoly*)))
-			  (< (cadr minpoly*) 2))
-		  (merror (intl:gettext "factor: second argument must be a nonlinear, univariate polynomial; found: ~M") *alpha*))
+			  (< (cadr minpoly*) 2)
+              ;; Detect a reducible polynomial: factor MINPOLY* with GAUSS = NIL,
+              ;; skip over the content and see if there is more than one factor
+              ;; or the single factor has a multiplicity > 1.
+              (let* ((pfac (let (gauss) (pfactor minpoly*)))
+                     (facs (if (pcoefp (car pfac)) (cddr pfac) pfac)))
+                (or (cddr facs) (> (cadr facs) 1))))
+		  (merror (intl:gettext "factor: second argument must be an irreducible, nonlinear, univariate polynomial; found: ~M") *alpha*))
 		(setq *alpha* (pdis (list (car minpoly*) 1 1))
 		      mm* (cadr minpoly*))
 		(unless (equal (caddr minpoly*) 1)
diff --git a/tests/rtest16.mac b/tests/rtest16.mac
index 3a2c49e6e..0d9c766d3 100644
--- a/tests/rtest16.mac
+++ b/tests/rtest16.mac
@@ -3282,6 +3282,14 @@ expand((1 + sqrt(2)) * 2^(15/4) + (1 - sqrt(2)) * 2^(5/4));
 (3^x + 3^(x + 1/2)) + 2*3^x;
 3^(x+1)+3^(x+1/2);
 
+/* Bug #4658: "factor should check that second argument is irreducible" */
+
+errcatch(factor(a^2*g+a*g-a^2, g^3-1));
+[];
+
+factor(a^2*g+a*g-a^2, second(factor(g^3-1)));
+(a*(-g+3*a+1)*(g-1))/3;
+
 kill(x);
 done$
 

-----------------------------------------------------------------------

Summary of changes:
 src/rat3e.lisp    | 10 ++++++++--
 tests/rtest16.mac |  8 ++++++++
 2 files changed, 16 insertions(+), 2 deletions(-)


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