[GiNaC-list] degree function

Thu Jul 4 21:46:16 CEST 2024

Thank you, Vladimir. It was a great suggestion. Your comments reflect the statement in section 4.5 of the tutorial.

"GiNaC will assign the symbol an internal, unique name of the form symbolNNN. This won’t affect the usability of the symbol but the output of your calculations will become more readable if you give your symbols sensible names....."

 My context was a bit different. I was trying to use the Lagrange interpolation theorem generically. I created three methods for basis, interpolation, and utility.
It was my ignorance to assume symbols are more like literals.

After your guidance, I passed the symbol from one function to another so that it could be used.

Beauty, now I do not have to add/subtract the coefficient of equal degree terms for which I was planning to write a method.

Thanks again. BTW, I am reading your paper "CLASSICAL/QUANTUM=COMMUTATIVE/NONCOMMUTATIVE?"

Regards,
Santos

________________________________
From: Vladimir V. Kisil <V.Kisil at leeds.ac.uk>
Sent: Wednesday, July 3, 2024 4:38 AM
To: GiNaC discussion list <ginac-list at ginac.de>; Santos Jha <sjha2 at gmu.edu>
Cc: Vladimir V. Kisil <V.Kisil at leeds.ac.uk>
Subject: Re: [GiNaC-list] degree function

        Hello,

        I think the problem is with your declaration of symb in
  subExpres.degree(symb). Did you get it from a string "x" through a
  parser? In this case it may be different from x in the poly. Then,
  it is absent from a monomial and its degree is indeed zero.
  Here is an output from a complete example code (see below):

----------------------------------------
Polynomial is x^2, it is a sum of monomials: false
x is polynomial=true and  degree=1
2 is polynomial=true and  degree=0

----------------------------------------
Polynomial is 1+3*x^2+2*x, it is a sum of monomials: true
3*x^2 is polynomial=true and  degree=2
2*x is polynomial=true and  degree=1
1 is polynomial=true and  degree=0

  Note that your polynomial is actually a monomial (but not a sum of
  monomials) and this situation needs to be treated differently.
  The complete code is:

#include <iostream>
#include <ginac/ginac.h>
using namespace std;
using namespace GiNaC;

int main() {

        realsymbol x("x");
        lst expressions = lst{-4*(-3+x)*(-1+x)+numeric(9,2)*(-2+x)*(-1+x)+numeric(1,2)*(-2+x)*(-3+x),
                3*pow(x,2)+2*x+1};

        for ( auto poly : expressions) {
                cout << endl << "----------------------------------------" << endl;

                poly = poly.expand();
                cout << "Polynomial is " << poly
                         << ", it is a sum of monomials: " << boolalpha << is_a<add>(poly)  <<endl;

                for (size_t i = 0; i != poly.nops(); ++i)   {  // Here poly is polynomial as above

                        ex subExpres=poly.op(i); // I get individual terms
                        cout << subExpres<< " is polynomial="<< is_polynomial(subExpres,x) ;
                        // GiNaC::ex pow2=pow(symb,2);
                        cout << " and  degree=" << subExpres.degree(x) << endl;
                }
        }

        return 0;
}

  Best wishes,
  Vladimir
--
Vladimir V. Kisil                  http://secure-web.cisco.com/1uavsA2G3CFg_3gcda5sStFEOvAflaJ2bvsS5fAGJLsvRhxmygxZpeJRcqg2QK_FVg34KGTN8REdXOdOooOeM8sgTWpZ3F67a-r3dX77zlhoiVmjogKWey3de4bHkriJs6vltoSgdKxnmVPR0q_Ciy5Yc8s7eUDeqz5rV8zpLyqHw7C6CzET3jV09f7-CfKMdNBBV1wIYsGFJcq3snZEYyonaLjZBVETNlCBifvTpvYyzGF5VGVLnOjgUg43ePKrNwYRJzHDL2LqYi2vnCvReRQ2yYcisllgfB6p2XaVaOApxnalBcI9HNzPeGWC5VyoF6psC0QWNquyN2LPh9zmQfht9vrx39ZgGFY0q9eBsWafhZyA7GjcOB4RciK_NThkyKIrQqs2y0tMsCz0f4uROcsslpK23m905FNZWgls-Zxyj3wn33HBUahBunSwQPFPw/http%3A%2F%2Fv-v-kisil.scienceontheweb.net
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>>>>> On Wed, 3 Jul 2024 03:19:30 +0000, Santos Jha <sjha2 at gmu.edu> said:

    SI> Greetings,

    SI> I am new to GiNac. I was trying to use the degree function, but
    SI> I got a weird result.

    SI> My initial expression is

    SI> -4*(-3+x)*(-1+x)+9/2*(-2+x)*(-1+x)+1/2*(-2+x)*(-3+x)

    SI> After the "expand" function call, it returns

    SI> 9/2*x^2-5/2*x-4*x^2+16*x-27/2*x+1/2*x^2

    SI> My goal is to add/subtract the coefficient of equal degree
    SI> terms. I could not find any function for that. ( if it is
    SI> already there, please point me) I wanted to write a function to
    SI> achieve it. To do so. I am taking each term and try to see if

    SI> for (size_t i = 0; i != poly.nops(); ++i) { // Here poly is
    SI> polynomial as above

    SI>             ex subExpres=poly.op(i); // I get individual terms
    SI> cout << "is polynomial="<< is_polynomial(subExpres,symb) <<endl;
    SI> // GiNaC::ex pow2=pow(symb,2); cout << subExpres<< " degree=" <<
    SI> subExpres.degree(symb) << endl;

    SI> }

    SI> It determines the subexpression as a polynomial but can not
    SI> determine the degree. E.g

    SI> is polynomial=1 9/2*x^2 degree=0 // Here degree returned is
    SI> wrong.

    SI> Your thoughts will be appreciated.  Regards, Santos

    SI> ----------------------------------------------------
    SI> Alternatives:

    SI> ----------------------------------------------------
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