From ecaa89be6e2a34ebfbf179cbe51bd07be715a1e2 Mon Sep 17 00:00:00 2001
From: Kwankyu Lee <ekwankyu@gmail.com>
Date: Tue, 17 Dec 2024 17:13:27 +0900
Subject: [PATCH] Remove expected_codim argument
---
.../rings/function_field/khuri_makdisi.pyx | 20 ++++++++++++++++++-
1 file changed, 19 insertions(+), 1 deletion(-)
diff --git a/src/sage/rings/function_field/khuri_makdisi.pyx b/src/sage/rings/function_field/khuri_makdisi.pyx
index aa64322b0ed..d32677bed6f 100644
--- a/src/sage/rings/function_field/khuri_makdisi.pyx
+++ b/src/sage/rings/function_field/khuri_makdisi.pyx
@@ -871,13 +871,31 @@ cdef class KhuriMakdisi_small(KhuriMakdisi_base):
sage: p2 = G.point(pl2 - b)
sage: -(-p1) == p1 # indirect doctest
True
+
+ Check that :issue:`39148` is fixed::
+
+ sage: # long time
+ sage: k.<x> = FunctionField(GF(17)); t = polygen(k)
+ sage: F.<y> = k.extension(t^4 + (14*x + 14)*t^3 + 9*t^2 + (10*x^2 + 15*x + 8)*t
+ ....: + 7*x^3 + 15*x^2 + 6*x + 16)
+ sage: infty1, infty2 = F.places_infinite()
+ sage: O = F.maximal_order()
+ sage: P = O.ideal((x + 1, y + 7)).divisor()
+ sage: D1 = 3*infty2 + infty1 - 4*P
+ sage: D2 = F.divisor_group().zero()
+ sage: J = F.jacobian(model='km-small', base_div=4*P)
+ sage: J(D1) + J(D2) == J(D1)
+ True
"""
cdef int d0 = self.d0
cdef int g = self.g
cdef Matrix w1, w2, w3, w4
w1 = self.mu_image(self.wV2, wd, self.mu_mat23, 4*d0 - g + 1)
- w2 = self.mu_preimage(self.wV3, w1, self.mu_mat23, d0)
+ # The row space of w2 represents H^0(O(2D_0 - D)), whose dimension is
+ # at least d0 - g + 1, and hence the codimension is at most d0. Thus,
+ # we cannot provide an expected_codim argument for mu_preimage.
+ w2 = self.mu_preimage(self.wV3, w1, self.mu_mat23)
# efficient than
# wf = matrix(w2[0])
# w3 = self.mu_image(wf, self.wV4, self.mu_mat24, 4*d0 - g + 1)