#11431: Conversion from Singular to Sage
--------------------------+-------------------------------------------------
   Reporter:  SimonKing   |          Owner:  was       
       Type:  defect      |         Status:  new       
   Priority:  major       |      Milestone:  sage-4.7.1
  Component:  interfaces  |       Keywords:            
Work_issues:              |       Upstream:  N/A       
   Reviewer:              |         Author:  Simon King
     Merged:              |   Dependencies:  #11316    
--------------------------+-------------------------------------------------
 On [http://groups.google.com/group/sage-
 support/browse_thread/thread/f35e6064434dacdc sage-devel], Francisco
 Botana complained about some shortcomings of the conversion from Singular
 (pexpect interface) to Sage.

 I think the conversions provided by this patch are quite thorough.

 First of all, the patch provides a conversion of base rings, even with
 minpoly, with complicated block, matrix and weighted orders (note that one
 needs #11316) and even quotient rings:
 {{{
 sage: singular.eval('ring r1 =
 (9,x),(a,b,c,d,e,f),(M((1,2,3,0)),wp(2,3),lp)')
 'ring r1 = (9,x),(a,b,c,d,e,f),(M((1,2,3,0)),wp(2,3),lp);'
 sage: R = singular('r1').sage_basering()
 sage: R
 Multivariate Polynomial Ring in a, b, c, d, e, f over Finite Field in x of
 size 3^2
 sage: R.term_order()
 Block term order with blocks:
 (Matrix term order with matrix
 [1 2]
 [3 0],
  Weighted degree reverse lexicographic term order with weights (2, 3),
  Lexicographic term order of length 2)

 sage: singular.eval('ring r3 = (3,z),(a,b,c),dp')
 'ring r3 = (3,z),(a,b,c),dp;'
 sage: singular.eval('minpoly = 1+z+z2+z3+z4')
 'minpoly = 1+z+z2+z3+z4;'
 sage: singular('r3').sage_basering()
 Multivariate Polynomial Ring in a, b, c over Univariate Quotient
 Polynomial Ring in z over Finite Field of size 3 with modulus z^4 + z^3 +
 z^2 + z + 1

 sage: singular.eval('ring r5 = (9,a), (x,y,z),lp')
 'ring r5 = (9,a), (x,y,z),lp;'
 sage: Q = singular('std(ideal(x^2,x+y^2+z^3))', type='qring')
 sage: Q.sage_basering()
 Quotient of Multivariate Polynomial Ring in x, y, z over Finite Field in a
 of size 3^2 by the ideal (y^4 - y^2*z^3 + z^6, x + y^2 + z^3)
 }}}

 By consequence, it is now straight forward to convert polynomials or
 ideals to sage:
 {{{
 sage: singular.eval('ring R = integer, (x,y,z),lp')
 '// ** You are using coefficient rings which are not fields...'
 sage: I = singular.ideal(['x^2','y*z','z+x'])
 sage: I.sage()  # indirect doctest
 Ideal (x^2, y*z, x + z) of Multivariate Polynomial Ring in x, y, z over
 Integer Ring

 # Note that conversion of a Singular string to a Sage string was missing
 sage: singular('ringlist(basering)').sage()
 [['integer'], ['x', 'y', 'z'], [['lp', (1, 1, 1)], ['C', (0)]], Ideal (0)
 of Multivariate Polynomial Ring in x, y, z over Integer Ring]

 sage: singular.eval('ring r10 = (9,a), (x,y,z),lp')
 'ring r10 = (9,a), (x,y,z),lp;'
 sage: Q = singular('std(ideal(x^2,x+y^2+z^3))', type='qring')
 sage: Q.sage()
 Quotient of Multivariate Polynomial Ring in x, y, z over Finite Field in a
 of size 3^2 by the ideal (y^4 - y^2*z^3 + z^6, x + y^2 + z^3)
 sage: singular('x^2+y').sage()
 x^2 + y
 sage: singular('x^2+y').sage().parent()
 Quotient of Multivariate Polynomial Ring in x, y, z over Finite Field in a
 of size 3^2 by the ideal (y^4 - y^2*z^3 + z^6, x + y^2 + z^3)
 }}}

-- 
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/11431>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica, 
and MATLAB

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