code: def correct_sign(deg_f, deg_g, s1, rdel, cdel):
      """
      Used in various subresultant prs algorithms.
  
      Evaluates the determinant, (a.k.a. subresultant) of a properly selected
      submatrix of s1, Sylvester's matrix of 1840, to get the correct sign
      and value of the leading coefficient of a given polynomial remainder.
  
      deg_f, deg_g are the degrees of the original polynomials p, q for which the
      matrix s1 = sylvester(p, q, x, 1) was constructed.
  
      rdel denotes the expected degree of the remainder; it is the number of
      rows to be deleted from each group of rows in s1 as described in the
      reference below.
  
      cdel denotes the expected degree minus the actual degree of the remainder;
      it is the number of columns to be deleted --- starting with the last column
      forming the square matrix --- from the matrix resulting after the row deletions.
  
      References
      ==========
      Akritas, A. G., G.I. Malaschonok and P.S. Vigklas: ``Sturm Sequences
      and Modified Subresultant Polynomial Remainder Sequences.''
      Serdica Journal of Computing, Vol. 8, No 1, 29-46, 2014.
  
      """
      M = s1[:, :]  # copy of matrix s1
  
      # eliminate rdel rows from the first deg_g rows
      for i in range(M.rows - deg_f - 1, M.rows - deg_f - rdel - 1, -1):
          M.row_del(i)
  
      # eliminate rdel rows from the last deg_f rows
      for i in range(M.rows - 1, M.rows - rdel - 1, -1):
          M.row_del(i)
  
      # eliminate cdel columns
      for i in range(cdel):
          M.col_del(M.rows - 1)
  
      # define submatrix
      Md = M[:, 0 : M.rows]
  
      return Md.det()
  
imports: from sympy.concrete.summations import summation
  from sympy.core.function import expand
  from sympy.core.numbers import nan
  from sympy.core.singleton import S
  from sympy.core.symbol import Dummy
  from sympy.functions.elementary.complexes import Abs, sign
  from sympy.functions.elementary.integers import floor
  from sympy.matrices.dense import eye, Matrix, zeros
  from sympy.printing.pretty.pretty import pretty_print
  from sympy.simplify.simplify import simplify
  from sympy.polys.domains import QQ
  from sympy.polys.polytools import degree, LC, Poly, pquo, quo, prem, rem
  from sympy.polys.polyerrors import PolynomialError
label_desc: Use image node_id 27 for calling a global function with example usage: correct_sign(deg_f, deg_g, s1, rdel, cdel) and returns: Md