March 2002 - PURRS-devel - BUGSENG Mailman

purrs src/rr_solver.cc tests/rrs_driver.cc
by Tatiana Zolo 07 Mar '02

07 Mar '02

CVSROOT: /cvs/purrs Module name: purrs Changes by: zolo(a)cs.unipr.it 2002-03-07 14:24:26 Modified files: src : rr_solver.cc tests : rrs_driver.cc Log message: Now the recurrence relation is expanded as soon as it is inserted by the user. Patches: http://www.cs.unipr.it/cgi-bin/cvsweb.cgi/purrs/src/rr_solver.cc.diff?cvsro… http://www.cs.unipr.it/cgi-bin/cvsweb.cgi/purrs/tests/rrs_driver.cc.diff?cv…

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Re: What is a polynomial in x?
by Roberto Bagnara 07 Mar '02

07 Mar '02

Christian Bauer wrote: > Hi! > > On Thu, Mar 07, 2002 at 12:58:59PM +0100, Roberto Bagnara wrote: > >> if (is_a_polynomial(e, x)) { >> > > if (e.info(info_flags::polynomial)) { > > (there's also info_flags::integer_polynomial and a couple of others; the > complete list is in the GiNaC tutorial) Hmmm... the notion of polynomial in x that is implemented by degree, ldegree, and so forth, is more general (and rightly so, we believe). For instance, sqrt(2)*x is a polynomial in x of degree 1 accordind to degree(), whereas the info() methods would simply classify is as a non-polynomial. I see two possibilities (but I may be wrong, of course): 1) it is illegal to say degree(sqrt(2)*x) and the fact that now this evaluates to the sensible value 1 is just an accident: it may stop working at any time. In other words, degree() and friends would be granted to work only for expressions e such that e.info(info_flags::polynomial) is true. 2) It is legal to say degree(sqrt(2)*x). But then it would be useful to precisely characterize the class of expressions e and x such that degree(e, x) is well defined. Am I missing something? Thanks a lot Roberto -- Prof. Roberto Bagnara Computer Science Group Department of Mathematics, University of Parma, Italy http://www.cs.unipr.it/~bagnara/ mailto:bagnara@cs.unipr.it

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What is a polynomial in x?
by Roberto Bagnara 07 Mar '02

07 Mar '02

We have some doubts on the handling of polynomials under GiNaC. The question we need to be answered is: what is, for GiNaC, a polynomial in a variable x? That is, for which class of expressions are the functions degree, ldegree, coeff, lcoeff, tcoeff... guaranteed to work? If this class is not the class of all expressions, it would be nice to have a function or method recognizing it so that one can do things like if (is_a_polynomial(e, x)) { // Here it is safe to use degree(e, x), ... } While we are trying to write code that depends only on the guarantees GiNaC offer, we would like to take the occasion of improving GiNaC's documentation (that is, if you answer nicely we will contribute a couple of paragraph for the section of the manual dealing with polynomials ;-) All the best Tatiana Zolo Roberto Bagnara -- Prof. Roberto Bagnara Computer Science Group Department of Mathematics, University of Parma, Italy http://www.cs.unipr.it/~bagnara/ mailto:bagnara@cs.unipr.it

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purrs/doc purrs.tex
by Alessandro Zaccagnini 07 Mar '02

07 Mar '02

CVSROOT: /cvs/purrs Module name: purrs Changes by: zaccagnini(a)cs.unipr.it 2002-03-07 10:16:21 Modified files: doc : purrs.tex Log message: 1. Corrected a few misprints; 2. Added precise references to theorems quoted in section 2.1.1; 3. Added remark on Example 3 of Cohen & Katcoff. Patches: http://www.cs.unipr.it/cgi-bin/cvsweb.cgi/purrs/doc/purrs.tex.diff?cvsroot=…

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purrs/src rr_solver.cc
by Tatiana Zolo 07 Mar '02

07 Mar '02

CVSROOT: /cvs/purrs Module name: purrs Changes by: zolo(a)cs.unipr.it 2002-03-07 09:42:37 Modified files: src : rr_solver.cc Log message: Fixed the problem about expansion of the polynomials when it is necessary. Patches: http://www.cs.unipr.it/cgi-bin/cvsweb.cgi/purrs/src/rr_solver.cc.diff?cvsro…

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purrs/src rr_solver.cc
by Tatiana Zolo 07 Mar '02

07 Mar '02

CVSROOT: /cvs/purrs Module name: purrs Changes by: zolo(a)cs.unipr.it 2002-03-07 08:57:38 Modified files: src : rr_solver.cc Log message: Fixed two errors: 1.When function 'solve' see if all the occurrences of `x(e)' are such that `e' is numeric. 2.In the binary case when we have double root. Patches: http://www.cs.unipr.it/cgi-bin/cvsweb.cgi/purrs/src/rr_solver.cc.diff?cvsro…

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purrs/tests rrs_driver.cc
by Tatiana Zolo 06 Mar '02

06 Mar '02

CVSROOT: /cvs/purrs Module name: purrs Changes by: zolo(a)cs.unipr.it 2002-03-06 13:18:25 Modified files: tests : rrs_driver.cc Log message: Added clause catch for the case of exceptions thrown with 'string' type. Patches: http://www.cs.unipr.it/cgi-bin/cvsweb.cgi/purrs/tests/rrs_driver.cc.diff?cv…

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purrs/src rr_solver.cc
by Tatiana Zolo 06 Mar '02

06 Mar '02

CVSROOT: /cvs/purrs Module name: purrs Changes by: zolo(a)cs.unipr.it 2002-03-06 12:39:42 Modified files: src : rr_solver.cc Log message: Fixed an error: the exponential's coefficient must be expanded when passed to the function sum_poly_times_exponentials(). Patches: http://www.cs.unipr.it/cgi-bin/cvsweb.cgi/purrs/src/rr_solver.cc.diff?cvsro…

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purrs src/rr_solver.cc tests/rrs_driver.cc
by Tatiana Zolo 06 Mar '02

06 Mar '02

CVSROOT: /cvs/purrs Module name: purrs Changes by: zolo(a)cs.unipr.it 2002-03-06 11:31:50 Modified files: src : rr_solver.cc tests : rrs_driver.cc Log message: Solve first order recurrence relation also with parameters. Patches: http://www.cs.unipr.it/cgi-bin/cvsweb.cgi/purrs/src/rr_solver.cc.diff?cvsro… http://www.cs.unipr.it/cgi-bin/cvsweb.cgi/purrs/tests/rrs_driver.cc.diff?cv…

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degree of non-expanded polynomials
by Alessandro Zaccagnini 06 Mar '02

06 Mar '02

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

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