August 2004 - GiNaC-list

Re: [GiNaC-list] quo behaviour
by Ralf Stephan 18 Aug '04

18 Aug '04

> I guess one needs to re-express quo()/rem() in terms of pquo()/prem() to > make that work? Only your question made me aware of prem(). Now, that seems possible but prem() itself appears to have problems: > prem(x*y^3,y*x^3,x); x*y^3 This would (according to the tutorial) satisfy x^(-3)*x*y^3 = y*x^3*q + prem (=x*y^3), so q = pquo() = (x^(-3)-1)*y^2/x^2 which doesn't seem right. There is also the problem of quo() returning a fail (decompose_rational() needs it) which surprised my computations, giving an error, something with commutativity, and I needed some time to see that I was working with a fail that I got from quo(). Thanks, ralf

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quo behaviour
by Ralf Stephan 17 Aug '04

17 Aug '04

Hello, sorry for bothering you so much, you probably think by now I get paid for this. The tutorial says that parameters to quo() should be univariate polynomials. Is this really necessary, esp. if you also get the main variable as parameter? Even if I accept the univariateness for parameters[*], the behaviour of the function towards multivariate input is inconsistent, as the ginsh session shows: > quo(y,y*x,y); FAIL > quo(y*x,y,y); x Thanks, ralf [*] I do not accept it, as I understand ginac from its interface to be inherently multivariate, except for the diff function, and even that is disputable.

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That series again
by Ralf Stephan 13 Aug '04

13 Aug '04

Using the new 1.2.3, in ginsh: > series((1+x)^y,x,5); 1+Order(x^5) while > series(exp(y*log(1+x)),x,5); 1+(y)*x+(-1/2*y+1/2*y^2)*x^2+(1/3*y-1/2*y^2+1/6*y^3)*x^3+(1/24*y^4-1/4*y+11/24*y^2-1/4*y^3)*x^4+Order(x^5) My understanding is the latter is correct as it gives 1/n! the Stirling1 triangle and substituting a number for y gives binomial coefficients. Maybe any expansion of a power can be expressed by such a construction, even in the GiNaC source, so a patch would be straightforward? ralf

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GiNaC 1.2.3
by Jens Vollinga 13 Aug '04

13 Aug '04

Hi, GiNaC 1.2.3 is out and available. The changes are: - improved handling of dirac / color algebra - fixed bug in series expansion of powers - fixed and improved configuration of documentation building As always, this release can be downloaded from ftp://ftpthep.physik.uni-mainz.de/pub/GiNaC/ Enjoy, Jens

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series segv
by Ralf Stephan 12 Aug '04

12 Aug '04

This bombs in ginsh: series((1+x)^y,x,5); Thanks, ralf

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tensor manipulation....
by Matt Bellis 06 Aug '04

06 Aug '04

Hi ginac'ers, Brand new to this, so sorry if this is old hat. Couldn't find it in the archives. I want to do some simple calculations involving 4-momenta and dirac matrices. Simplest case I want to get the invariant mass of a 4-momentum. I've got this for now. #include<iostream> #include<ginac/ginac.h> using namespace std; using namespace GiNaC; int main() { symbol mu_sym("mu"); varidx mu(mu_sym, 4); symbol p1_sym("p1"); ex p1 = indexed(p1_sym, mu); symbol p2_sym("p2"); ex p2 = indexed(p2_sym, mu.toggle_variance()); ex mass = p1 * p2; cerr << mass << endl; return 0; } It looks OK, but I need to be able to enter in data for p1 and p2 so I can calculate the mass. I don't know how to do this. Anyone know? Also, right now I've got two separate expressions for the raised and lowered indices of the momentum (p1, p2). Is there an easier way to do this? Thanks in advance for any help anyone can offer. -- --------------------------- Matt Bellis Carnegie Mellon University (office) 412-268-6949 (cell) 412-310-4586 ---------------------------

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Presumably...
by Richard B. Kreckel 06 Aug '04

06 Aug '04

...the bottle of Champagne has already been emptied and the hangover is gone. This is because GiNaC release 1.2.2 has hit the FTP-server the day before yesterday. We apologize for not having sent out invitations for the release party to the public. Some of us simply couldn't afford spending tons of money on beverages for the VIPs (like we usually do). Anyways, here's the beef: * Added const_preorder_iterator and const_postorder_iterator classes (and associated methods ex::pre/postorder_begin/end()) providing tree traversal with iterators. * Fixed the LaTeX output of the varidx class. * Fixed bugs in series expansion and complex conjugation. * (p.i*p.i).get_free_indices() returns the correct result () instead of (.i). * Symbolic functions without any eval(), evalf() etc. functions now work properly. * integer_content(), content(), and primpart() now also work for polynomials with rational coefficients (calculating the LCM of coefficients' denominators). * Added method matrix::rank(). * Added function resultant(). * Added integer_content() function to ginsh. Enjoy! -richy. (Christian, I got an idea: bottle party next time!) -- Richard B. Kreckel <http://www.ginac.de/~kreckel/>

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'full' differentiation?
by Ralf Stephan 02 Aug '04

02 Aug '04

Hello, is there an easy way to get 'full' differentiation, ie, of all variables, instead of only the main variable? Example: Given symbols x,u, diff(x/u, x) would then produce (u-u'x)/u^2. At the moment, I'm abusing psi to get the effect but that is certainly not the best way. sincerely, ralf

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get_free_indices() returns wrong result
by varg＠thsun1.jinr.ru 02 Aug '04

02 Aug '04

Hello! This simple program: #include <iostream> #include <ginac/ginac.h> using namespace std; using namespace GiNaC; int main(int argc, char** argv) { symbol A("A"); symbol i_sym("i"); idx i(i_sym, 3); ex test = indexed(A, i)*indexed(A,i); exprseq free_ind = test.get_free_indices(); cout << "Free indices of expression " << test << ": "; cout << free_ind << endl; return 0; } gives: Free indices of expression (A.i)^2: (.i) but not just an empty sequence, as I expected. This patch seems to fix the inconsistency: diff -u -r GiNaC-orig/ginac/indexed.cpp GiNaC/ginac/indexed.cpp --- GiNaC-orig/ginac/indexed.cpp 2004-06-10 02:19:36.000000000 +0400 +++ GiNaC/ginac/indexed.cpp 2004-07-26 22:31:52.000000000 +0400 @@ -499,10 +499,31 @@ return free_indices; } +// checks if index is symbolic and is_exactly_a<idx> +struct is_a_symb_idx : public std::unary_function<ex, bool> { + bool operator()(const ex & e) + { + return is_exactly_a<idx>(e) && ex_to<idx>(e).is_symbolic(); + } +}; + exvector power::get_free_indices() const { - // Return free indices of basis - return basis.get_free_indices(); + exvector tmp_inds = basis.get_free_indices(); + + if (exponent.info(info_flags::even)) { + // if the exponent is an even number, then any "free" index + // of base is actually a dummy index, if it + // 1) has no variance, + // 2) is not a numeric index + exvector really_free; + remove_copy_if(tmp_inds.begin(), tmp_inds.end(), + back_inserter(really_free), is_a_symb_idx()); + return really_free; + } else { + return tmp_inds; + } + } /** Rename dummy indices in an expression.

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