[GiNaC-list] subscripted variables

[Vladimir V. Kisil]

	Good day, Marko,
>>>>> On Mon, 6 Feb 2023 06:18:11 +0100, Marko Riedel <riedelmo at mathematik.uni-stuttgart.de> said:

    MR> Post Scriptum. I managed to get the subscripts by subclassing
    MR> the symbol class to attach an integer to it. Still I wonder if
    MR> that is the best way to go about it.

    It depends on your purpose, why do you need integer associated to
  symbols? An alternative solution to keep a C++
  std::map<GiNaC::ex, int>
  which will be  a dictionary converting symbols to respective
  indices. Or consider a usage of GiNaC::indexed

	ex a=symbol("a"), i=symbol("i");
	ex ai=indexed(a, idx(i,4));
	ex a1=ai.subs(i==1);
	ex a2=ai.subs(i==2);
	ex a3=ai.subs(i==3);
	
	ex e = 2*pow(a1, 2) + 3*a1*a2 + 4*pow(a2, 3);
	cout << e << endl;
	// -> 4*(a.2)^3+3*a.1*a.2+2*(a.1)^2
	cout << a2.op(1).op(0)  << endl;
	// -> 2
	for  (int j=1; j < 4; ++j)
		cout << "Variable with index " << j  << " has degree " << e.degree(ai.subs(i == j)) << endl;
	/* 
	   -> Variable with index 1 has degree 2
	   -> Variable with index 2 has degree 3
	   -> Variable with index 3 has degree 0
	*/

  The example also suggests a solution to your other question:

    MR> Am 05.02.23 um 23:07 schrieb Marko Riedel:
    >> better way.  I am also looking for a means of extracting a set of
    >> variables that are present in a polynomial, or the degree these
    >> variables have.

  Best wishes,
  Vladimir
-- 
Vladimir V. Kisil                 http://www1.maths.leeds.ac.uk/~kisilv/
  Book:      Geometry of Mobius Maps       https://doi.org/10.1142/p835
  Soft:      Geometry of cycles         http://moebinv.sourceforge.net/
  Jupyter notebooks:        https://github.com/vvkisil?tab=repositories