degree of non-expanded polynomials

6 Mar 2002

      I have been experimenting with GiNaC, and I found that on page 46,
section 
5.5.2, of the manual (version 1.0.6) that degree() works reliably also 
on non-expanded polynomials. But the following program seems to prove 
that it is not the case. 

#include <iostream>
#include <ginac/ginac.h>

using namespace std;
using namespace GiNaC;

typedef GiNaC::ex GExpr;
typedef GiNaC::symbol GSymbol;

int main() {
  GSymbol x("x");

  GExpr h_a = numeric(1,2) * x * (x-1);
  GExpr h_b = - (x+1) * (x-1);
  GExpr h_c = numeric(1,2) * x * (x+1);

  GExpr p = h_a + h_b + h_c;
  std::cout << "p = " << p << "  degree " << p.degree(x) << std::endl;
  p = p.expand();
  std::cout << "p = " << p << "  degree " << p.degree(x) << std::endl;
  return 0;
}

This is the output that I obtained (from version 1.0.5):

p = 1/2*(1+x)*x+1/2*(-1+x)*x+(-1+x)*(-1-x)  degree 2
p = 1  degree 0

Best wishes 

Alessandro Zaccagnini
The purrs developers team at the University of Parma