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[bug] pi example program does not report correct accuracy
by xt knight 28 Jul '07

28 Jul '07

This is a simple bug and it's reproducible on every machine. Using the pi example in libcln (./examples), type this: pi 5 3.1415927 is not 5 digits. pi 1 3.1416 is not 1 digit. https://bugs.launchpad.net/debian/+source/cln/+bug/128851 This bug reporter also mentions that it rounds the last number and that's not documented anywhere. Thank you for your time, xtknight

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Re: GiNaC-list Digest, Vol 29, Issue 1
by Jan Bos 25 Jul '07

25 Jul '07

Dear Richard, Thanks for the prompt reply. I'm no expert and not aware of LIA-3. Maybe you could give me a reference as where to obtain it? The reason I posted the question is that since GiNaC is embedded in C++ (beautiful concept by the way) it seems odd to have different definitions for the case at hand. Of course I can't oversee the consequences of a change, it would be convenient to code decisions based on the argument in a uniform way though. Best regards Jan Bos On Sun, 2007-07-22 at 12:00 +0200, ginac-list-request(a)ginac.de wrote: > Send GiNaC-list mailing list submissions to > ginac-list(a)ginac.de > > To subscribe or unsubscribe via the World Wide Web, visit > https://www.cebix.net/mailman/listinfo/ginac-list > or, via email, send a message with subject or body 'help' to > ginac-list-request(a)ginac.de > > You can reach the person managing the list at > ginac-list-owner(a)ginac.de > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of GiNaC-list digest..." > > > Today's Topics: > > 1. atan2(0,-4) = -Pi? (Jan Bos) > 2. Re: atan2(0,-4) = -Pi? (Richard B. Kreckel) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Sat, 21 Jul 2007 21:24:57 +0200 > From: Jan Bos <jb68(a)xs4all.nl> > Subject: [GiNaC-list] atan2(0,-4) = -Pi? > To: ginac-list(a)ginac.de > Message-ID: <1185045897.9600.20.camel@jbos1> > Content-Type: text/plain > > Dear All, > > Is there a reason for GiNaC (or ginsh) to evaluate > atan2(0,-4) as -Pi instead of +Pi the definition used by for instance > C/C++? Looking at the code, inifcns_trans.cpp last shown case below, > explicitly states it should. Or can I expect it to be changed in the > future? > > static ex atan2_eval(const ex & y, const ex & x) > { > if (y.info(info_flags::numeric) && x.info(info_flags::numeric)) { > > if (y.is_zero()) { > > // atan(0, 0) -> 0 > if (x.is_zero()) > return _ex0; > > // atan(0, x), x real and positive -> 0 > if (x.info(info_flags::positive)) > return _ex0; > > // atan(0, x), x real and negative -> -Pi > if (x.info(info_flags::negative)) > return _ex_1*Pi; > } > > ... > > The code fragment is from version 1.3.7 > > best regards > > Jan Bos > > > > > > ------------------------------ > > Message: 2 > Date: Sun, 22 Jul 2007 01:16:38 +0200 > From: "Richard B. Kreckel" <kreckel(a)ginac.de> > Subject: Re: [GiNaC-list] atan2(0,-4) = -Pi? > To: GiNaC discussion list <ginac-list(a)ginac.de> > Message-ID: <46A293D6.9040301(a)ginac.de> > Content-Type: text/plain; charset=ISO-8859-1; format=flowed > > Dear Jan, > > Jan Bos wrote: > > Is there a reason for GiNaC (or ginsh) to evaluate > > atan2(0,-4) as -Pi instead of +Pi the definition used by for instance > > C/C++? Looking at the code, inifcns_trans.cpp last shown case below, > > explicitly states it should. Or can I expect it to be changed in the > > future? > > > > static ex atan2_eval(const ex & y, const ex & x) > > { > > if (y.info(info_flags::numeric) && x.info(info_flags::numeric)) { > > > > if (y.is_zero()) { > > > > // atan(0, 0) -> 0 > > if (x.is_zero()) > > return _ex0; > > > > // atan(0, x), x real and positive -> 0 > > if (x.info(info_flags::positive)) > > return _ex0; > > > > // atan(0, x), x real and negative -> -Pi > > if (x.info(info_flags::negative)) > > return _ex_1*Pi; > > } > > > > I don't suppose anybody lightly intends to change such definitions. :) > > Well, I looked in my notes and didn't find anything motivating that > choice for atan2. > > I recall that back when I wrote this, CLTL 2nd edition provided guidance > when choosing branch cuts of single-argument functions in the complex > domain. And later at some point I realized that the C99 standard agrees > with CLTL for all single-argument functions. (That appeared to be too > good to be true, but it is true.) Nobody was aware of LIA-3 at that time > but I'm quite sure that all of GiNaC's single-argument functions agree > with LIA-3, simply because they agree with C99. > > Our two-argument function atan2, however, may never have been checked > against any standard. I just did that with C99 and CLTL, and they both > specify atan2(0,-4) to be +Pi, indeed. Maybe, we ought to change this? > Before we do so: What does LIA-3 say? > > Our choice may be bad but I frankly admit that I don't know why +Pi is > any better than -Pi, or a more symmetric choice a la Mathematica like > atan2(0,x>0)=Pi/2, atan2(0,x<0)=-Pi/2, or 0 for all x. Can you explain > that choice? > > Cheers > -richy. > > PS: In any case, this is a good lesson how not to write comments, sigh. > -- > Richard B. Kreckel > <http://www.ginac.de/~kreckel/> > > > ------------------------------ > > _______________________________________________ > GiNaC-list mailing list > GiNaC-list(a)ginac.de > https://www.cebix.net/mailman/listinfo/ginac-list > > > End of GiNaC-list Digest, Vol 29, Issue 1 > ***************************************** >

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atan2(0,-4) = -Pi?
by Jan Bos 22 Jul '07

22 Jul '07

Dear All, Is there a reason for GiNaC (or ginsh) to evaluate atan2(0,-4) as -Pi instead of +Pi the definition used by for instance C/C++? Looking at the code, inifcns_trans.cpp last shown case below, explicitly states it should. Or can I expect it to be changed in the future? static ex atan2_eval(const ex & y, const ex & x) { if (y.info(info_flags::numeric) && x.info(info_flags::numeric)) { if (y.is_zero()) { // atan(0, 0) -> 0 if (x.is_zero()) return _ex0; // atan(0, x), x real and positive -> 0 if (x.info(info_flags::positive)) return _ex0; // atan(0, x), x real and negative -> -Pi if (x.info(info_flags::negative)) return _ex_1*Pi; } ... The code fragment is from version 1.3.7 best regards Jan Bos

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Expression order changing
by Martin Sandve Alnæs 05 Jun '07

05 Jun '07

Hi, when generating code from ginac expressions (with csrc), the order of the printed expressions will vary depending on previous operations in the program, in particular the previous construction of symbols. I understand this is because ginac uses an internal symbol id counter of some kind. Is it possible to "reset" this counter, or somehow make sure a set of newly created symbols keep the same relative order independent of previous operations in the program? It would save us a tremendous amount of recompilation and code verification if we could do this. -- --- Martin Sandve Alnæs PhD student, Cardiac Computations Simula Research Laboratory, Norway

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Problem simplifying exponents in polynomials
by Gerry Boland 05 Jun '07

05 Jun '07

Hi all, I'm fairly new to GiNaC, but it's most impressive so far. But I've a problem, I'm struggling to perform the following: I have a polynomial with lots of terms (beta,e,t1 & t2 are realsymbols) like: 1/6+1/36*e^(-beta)*e^t1*e^(-t1)+1/36*e^(-t1)*e^(-beta)*e^t1+ 25/36*e^t1*e^(-beta)*e^(-t1)-1/36*e^(-t1)-1/36*e^(-t1)- 1/36*e^t1*e^(-beta)-1/36*e^t1*e^(-beta)-1/36*e^(-beta)*e^t1+ 5/36*e^(-t1)-1/36*e^(-t1)+1/36*e^(-t1)*e^t1*e^(-beta)- 1/36*e^(-t1)+1/36*e^(-beta)*e^(-t1)*e^t1-1/36*e^(-beta)*e^t1- 1/36*e^(-beta)*e^t1+1/36*e^t1*e^(-t1)*e^(-beta)-1/36*e^(-t1)+ 5/36*e^t1*e^(-beta) which should simply evaluate to: 1/6+5/6*e^(-beta) I've not managed to make the expand() & collect() functions do this, it seems to not want to perform something like: e^t*e^(1-t)=e^1 I also tried this using actual exp() instead of e^ symbol, but I found it harder to collect terms then too. Is there something I'm missing or doing wrong? Many thanks in advance, -Gerry

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Simplify clifford expresion: Works?
by Javier Ros Ganuza 29 May '07

29 May '07

NOTE: I'm using one week old CVS version. I'm playing with rotations in Cl3, following with my previous mail basis definition. I'm implementing the following trivial rotation ex R=(cos(theta/2)*dirac_ONE(0)-e00*e01*sin(theta/2)); cout << "subs Rotation R * e00 * R^\\dag = " << canonicalize_clifford((R * e00 * clifford_star(R)).expand()) << endl; That wonderfully (wonderfully!!!) gives: Rotation R * e00 * R^\dag = 2*e~1*sin(1/2*theta)*cos(1/2*theta)-sin(1/2*theta)^2*e~0 +e~0*cos(1/2*theta)^2 I'm trying to trigonometrically simmplify, 2*cos(1/2*theta)*e~1*sin(1/2*theta) -----to---> sin(theta) To that end: cout << "subs Rotation R * e00 * R^\\dag = " << canonicalize_clifford((R * e00 * clifford_star(R)).expand()).subs(lst(2*sin(1/2*theta)*cos(1/2*theta)==sin(theta))) << endl; that gives subs Rotation R * e00 * R^\dag = 2*e~1*sin(1/2*theta)*cos(1/2*theta)+e~(sin(theta))*cos(1/2*theta)^2-sin(1/2*theta)^2*e~(sin(theta)) Also, if I use cout << "subs Rotation R * e00 * R^\\dag = " << canonicalize_clifford((R * e00 * clifford_star(R)).expand()).subs(lst(2*sin(1/2*theta)*cos(1/2*theta)==sin(theta)),subs_options::algebraic) << endl; I get the same result subs Rotation R * e00 * R^\dag = 2*e~1*sin(1/2*theta)*cos(1/2*theta)+e~(sin(theta))*cos(1/2*theta)^2-sin(1/2*theta)^2*e~(sin(theta)) I think this is a bug. ???? Have a nice weekend! Javier

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real and imaginary parts of an expression
by Martin DRUON 28 May '07

28 May '07

hello, I would like to know how I can get the real part and the imaginary part of an expression (GiNaC::ex)... for example : #include <iostream> #include <ginac/ginac.h> using namespace GiNaC; int main(int argc, char **argv) { symbol x("x"), y("y"); // My complex number : x + iy symbol Q("Q"), a("a"); // Parameters // My expression ex f = (Q / 2 * Pi) * log(((x + I * y) - a) / ((x + I * y) + a)); std::cout << f << std::endl; // f.real() -> How I can get real part ??? // f.imag() -> How I can get imaginary part ??? return EXIT_SUCCESS; } Is it possible easily ? Thanks Martin

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How can I get a GiNaC::ex's name
by Zhongxing Xu 25 May '07

25 May '07

Hello, Say I construct an ex by: GiNaC::ex E(GiNaC::symbol("abc")); How can I get back "abc" from E as a C++ string or char*? Now I do this by print the ex to a std::ostringstream, and get the string from the ostringstream. Thanks. -- Zhongxing Xu

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Exterior algebra tools?
by Abraham D. Smith 24 May '07

24 May '07

After finding Maple inflexible and temperamental, I am interested in using GiNaC for some computations in exterior differential systems. I've read through the documentation fairly carefully, but I haven't seen any routines for working with exterior differential forms so far. Has anyone written a library to deal with alternating forms, including things like wedge-products, exterior differentiation, Lie derivatives (via Cartan's formula), and left-hook (inner product with vectors)? Thanks, Abe Smith (Duke University)

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Stuttgart.
by unknown＠example.com 19 May '07

19 May '07

Greetings. This is to ask whether there are any GiNaC users or developers in the Stuttgart (Germany) area. Thanks! Best regards, Marko Riedel -- +-------------------------------------------------------------+ | Marko Riedel, EDV Neue Arbeit gGmbH, markoriedelde(a)yahoo.de | | http://www.geocities.com/markoriedelde/index.html | +-------------------------------------------------------------+

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