[GiNaC-list] degree function

[Vladimir V. Kisil]

	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://v-v-kisil.scienceontheweb.net
  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
>>>>> 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



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