Atoms of an expression

[Christian Bauer]

Hi!

On Mon, Jun 09, 2003 at 04:17:54PM +0100, Dr. Vassilis S. Vassiliadis wrote:
> How is it possible to get GiNaC to yield all the 
> atoms occuring in an expression? (i.e. return a
> list of all the leaves of the expression tree).

This should be the easiest way:

void collect_atoms(const ex & e, lst & atoms)
{
    if (e.nops() == 0)
        atoms.append(e);
    else
        for (size_t i = 0; i < e.nops(); ++i)
            collect_atoms(e.op(i), atoms);
}
                                                                                
lst atoms_of(const ex & e)
{
    lst atoms;
    collect_atoms(e, atoms);
    atoms.sort();
    atoms.unique();
    return atoms;
}

symbol x("x"), y("y");
ex e = 3 * y * pow(x, 2) + sin(x + Pi/2);
cout << e << endl;
 // 3*y*x^2+sin(1/2*Pi+x)
cout << atoms_of(e) << endl;
 // {3,2,y,Pi,1/2,x}

Bye,
Christian

-- 
  / Physics is an algorithm
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