[GiNaC-devel] A patch for add::coeff() and new clifford_max_label()

[Vladimir Kisil]

		Dear Jens,

		I see the point. To add a puzzle I play with the following test:

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

int main(){
	realsymbol a("a"), b("b"), c("c"), d("d");
	varidx nu(symbol("nu", "\\nu"), 2), mu(symbol("mu", "\\mu"), 2);
	try {
		//cout << latex;
		ex e = 2*a*b*c*dirac_gamma(nu,1) + 2*dirac_gamma(nu,1)*b*b*a*a;
		cout << e.collect(dirac_gamma(nu,1)) << endl;
		// -> gamma~nu*(2*c*b*a+2*b^2*a^2) [OK]

		e = a*d*dirac_gamma(mu,2)*b*b*a*a* dirac_gamma(nu,1) 
			+ b*c*dirac_gamma(nu,1)*d*a+ sin(a)*c*dirac_gamma(nu,1)*abs(b)*b;
		cout << e.collect(dirac_gamma(nu,1)) << endl;
		//-> (c*ONE*b*sin(a)*abs(b)+d*c*ONE*b*a+d*gamma~mu*b^2*a^3)*gamma~nu [OK]
		e = d*dirac_gamma(mu,2) * dirac_gamma(nu,1) + a*b*c*dirac_gamma(nu,1);
		cout << e.collect(dirac_gamma(nu,1)) << endl;
		//-> gamma~nu*c*b*a+gamma~nu*(d*gamma~mu+c*ONE*b*a)-gamma~nu*c*ONE*b*a [Ugly!]

		// Just change representation label of dirac_gamma(mu,1) make iprovement
		e = d*dirac_gamma(mu,1) * dirac_gamma(nu,1) + a*b*c*dirac_gamma(nu,1);
		cout << e.collect(dirac_gamma(nu,1)) << endl;
		//-> (d*gamma~mu+c*ONE*b*a)*gamma~nu [Again OK!??]
	} catch  (exception &p) {
			cerr << "Got problem: " <<  p.what() << endl;
	}
}

  In the third out the expression gamma~nu*c*b*a-gamma~nu*c*ONE*b*a is
  not simplified to 0 automatically, although this disappear in the
  fourth output if all Clifford entries has the same representation
  label. 

  Just in case my previous patch may be of some use I would like to give
  another version of it. The function clifford_max_label() returns now
  "char" not "ex" which seems more natural. I think that function may be
  useful in clifford.cpp anyway.

  By the way, considering commutativity-noncommutative in GiNaC I
  realised that all symbols are assumed commutative. Is it difficult to
  add a new class of noncommutative symbols?

  Best wishes,
  Vladimir
-- 
Vladimir V. Kisil     email: kisilv at maths.leeds.ac.uk
--                      www: http://maths.leeds.ac.uk/~kisilv/


Index: ginac/clifford.h
===================================================================
RCS file: /home/cvs/GiNaC/ginac/clifford.h,v
retrieving revision 1.57
diff -r1.57 clifford.h
287a288,294
> /** Returns the maximal representation label of a clifford object 
>  *  if e contains at least one, otherwise returns -1 
>  *
>  *  @param e Expression to be processed
>  *  @ignore_ONE defines if clifford_ONE should be ignored in the search*/
> char clifford_max_label(const ex & e, bool ignore_ONE = false);
Index: ginac/clifford.cpp
===================================================================
RCS file: /home/cvs/GiNaC/ginac/clifford.cpp,v
retrieving revision 1.88
diff -r1.88 clifford.cpp
1035a1084,1099
> char clifford_max_label(const ex & e, bool ignore_ONE)
> {
> 	if (is_a<clifford>(e))
> 		if (ignore_ONE && is_a<diracone>(e.op(0)))
> 			return -1;
> 		else
> 			return ex_to<clifford>(e).get_representation_label();
> 	else {
> 		char rl = -1;
> 		for (size_t i=0; i < e.nops(); i++) 
> 			rl = (rl > clifford_max_label(e.op(i), ignore_ONE)) ? rl : clifford_max_label(e.op(i), ignore_ONE);
> 		return rl;
> 	}
> }
> 
Index: ginac/add.cpp
===================================================================
RCS file: /home/cvs/GiNaC/ginac/add.cpp,v
retrieving revision 1.76
diff -r1.76 add.cpp
31a32
> #include "clifford.h"
293a295,297
> 	std::auto_ptr<epvector> coeffseq_cliff(new epvector);
>  	char rl = clifford_max_label(s);
>  	bool do_clifford = (rl != -1), nonscalar = false;
299c303,310
< 		if (!restcoeff.is_zero())
---
>  		if (!restcoeff.is_zero()) {
>  			if (do_clifford) 
>  				if (clifford_max_label(restcoeff) == -1) 
>  					coeffseq_cliff->push_back(combine_ex_with_coeff_to_pair(ncmul(restcoeff, dirac_ONE(rl)), i->coeff));
>  				else {
>  					coeffseq_cliff->push_back(combine_ex_with_coeff_to_pair(restcoeff, i->coeff));
> 					nonscalar = true;
>  				}
300a312
> 		}
304c316,317
< 	return (new add(coeffseq, n==0 ? overall_coeff : _ex0))->setflag(status_flags::dynallocated);
---
> 	return (new add(nonscalar? coeffseq_cliff : coeffseq, 
> 					n==0 ? overall_coeff : _ex0))->setflag(status_flags::dynallocated);