gh-35045: Convert result of multivariate polynomial evaluation into c…

…orrect parent

    
Importing trac/u/roed/incorrect_parent_when_evaluating_constant_multivar
iate_polynomial...

(meant to fix #33373)
    
URL: #35045
Reported by: Marc Mezzarobba
Reviewer(s): Marc Mezzarobba, Travis Scrimshaw

src/sage/modular/modform_hecketriangle/graded_ring_element.py

@@ -1566,7 +1566,9 @@ def _q_expansion_cached(self, prec, fix_d, subs_d, d_num_prec, fix_prec = False)
  Y = SC.f_i_ZZ().base_extend(formal_d.parent())
 
  if (self.parent().is_modular()):
- qexp = self._rat.subs(x=X, y=Y, d=formal_d)
+ # z does not appear in self._rat but we need to specialize it for
+ # the evaluation to land in the correct parent
+ qexp = self._rat.subs(x=X, y=Y, z=0, d=formal_d)
  else:
  Z = SC.E2_ZZ().base_extend(formal_d.parent())
  qexp = self._rat.subs(x=X, y=Y, z=Z, d=formal_d)

src/sage/rings/polynomial/multi_polynomial_libsingular.pyx

@@ -2057,7 +2057,18 @@ cdef class MPolynomial_libsingular(MPolynomial):
  9
  sage: a.parent() is QQ
  True
+
+ See :trac:`33373`::
+
+ sage: k.<a> = GF(2^4)
+ sage: R.<x> = PolynomialRing(k, 1)
+ sage: f = R(1)
+ sage: S.<y> = PolynomialRing(k, 1)
+ sage: f(y).parent()
+ Multivariate Polynomial Ring in y over Finite Field in a of size 2^4
  """
+ cdef Element sage_res
+
  if len(kwds) > 0:
  f = self.subs(**kwds)
  if len(x) > 0:
@@ -2076,29 +2087,28 @@ cdef class MPolynomial_libsingular(MPolynomial):
  if l != parent._ring.N:
  raise TypeError("number of arguments does not match number of variables in parent")
 
+ res_parent = coercion_model.common_parent(parent._base, *x)
+ cdef poly *res # ownership will be transferred to us in the else block
  try:
  # Attempt evaluation via singular.
  coerced_x = [parent.coerce(e) for e in x]
  except TypeError:
  # give up, evaluate functional
- y = parent.base_ring().zero()
+ sage_res = parent.base_ring().zero()
  for (m,c) in self.dict().iteritems():
- y += c*mul([ x[i]**m[i] for i in m.nonzero_positions()])
- return y
-
- cdef poly *res # ownership will be transferred to us in the next line
- singular_polynomial_call(&res, self._poly, _ring, coerced_x, MPolynomial_libsingular_get_element)
- res_parent = coercion_model.common_parent(parent._base, *x)
-
- if res == NULL:
- return res_parent(0)
- if p_LmIsConstant(res, _ring):
- sage_res = si2sa( p_GetCoeff(res, _ring), _ring, parent._base )
- p_Delete(&res, _ring) # sage_res contains copy
+ sage_res += c * mul([x[i] ** m[i] for i in m.nonzero_positions()])
  else:
- sage_res = new_MP(parent, res) # pass on ownership of res to sage_res
+ singular_polynomial_call(&res, self._poly, _ring, coerced_x, MPolynomial_libsingular_get_element)
+
+ if res == NULL:
+ return res_parent(0)
+ if p_LmIsConstant(res, _ring):
+ sage_res = si2sa( p_GetCoeff(res, _ring), _ring, parent._base )
+ p_Delete(&res, _ring) # sage_res contains copy
+ else:
+ sage_res = new_MP(parent, res) # pass on ownership of res to sage_res
 
- if parent(sage_res) is not res_parent:
+ if sage_res._parent is not res_parent:
  sage_res = res_parent(sage_res)
  return sage_res
 

src/sage/schemes/riemann_surfaces/riemann_surface.py

@@ -2128,6 +2128,7 @@ def rigorous_line_integral(self, upstairs_edge, differentials, bounding_data):
  # CCzg is required to be known as we need to know the ring which the minpolys
  # lie in.
  CCzg, bounding_data_list = bounding_data
+ CCz = CCzg.univariate_ring(CCzg.gen(1)).base_ring()
 
  d_edge = tuple(u[0] for u in upstairs_edge)
  # Using a try-catch here allows us to retain a certain amount of back
@@ -2193,7 +2194,7 @@ def local_N(ct, rt):
  z_1 = a0lc.abs() * prod((cz - r).abs() - rho_z for r in a0roots)
  n = minpoly.degree(CCzg.gen(1))
  ai_new = [
- (minpoly.coefficient({CCzg.gen(1): i}))(z=cz + self._CCz.gen(0))
+ CCz(minpoly.coefficient({CCzg.gen(1): i}))(z=cz + self._CCz.gen(0))
  for i in range(n)
  ]
  ai_pos = [self._RRz([c.abs() for c in h.list()]) for h in ai_new]

src/sage/schemes/toric/points.py

@@ -849,7 +849,7 @@ def inhomogeneous_equations(self, ring, nonzero_coordinates, cokernel):
  z = [ring.zero()] * nrays
  for i, value in zip(nonzero_coordinates, z_nonzero):
  z[i] = value
- return [poly(z) for poly in self.polynomials]
+ return [poly.change_ring(ring)(z) for poly in self.polynomials]
 
  def solutions_serial(self, inhomogeneous_equations, log_range):
  """