July 2011 - GiNaC-list

Forge it !. WAS: Re: Weird: symbol * ddq_i, my_ex.subs((*ddq_i)==0) my_ex.subs(*ddq_i==0)my_ex.subs(symbol(*ddq_i)==0) ??
by Javier Ros 28 Jul '11

28 Jul '11

Sorry for disturbing, I solved the problem. For if some body is interested: I use a class symbol_numeric derived from symbol. the expression that was offending was conceptually of the type my_expression = symbol * (my_symbol_numeric) +my_symbol_numeric the result didn't simplified. I suppose this is CORRECT BEHAVIOR. My fault was the typecast removing it or changing it to symbol_numeric, solves the problem. That's why my_expression.subs(lst(symbol(my_symbol_numeric)==0,my_symbol_numeric ==0)) was needed. Now standard simplification my_expression.subs(my_symbol_numeric ==0) works. so I think the problem was related, although in a really involved manner, to the symbol factory known issue referred in GiNaC's Tutorial. Thank you again, Javier On Wed, Jul 27, 2011 at 11:09 PM, Javier Ros <jros(a)unavarra.es> wrote: > Jens, > > On Wed, Jul 27, 2011 at 8:41 PM, Jens Vollinga > <jens.vollinga(a)googlemail.com> wrote: >> Hi Javier, >> >> your information is a bit confusing. First you write: >> > I'm sorry. > >> On 27.07.2011 19:23, Javier Ros wrote: >>> >>> the following trivial simplifications >>> >>> my_ex.subs((*ddq_i)==0) >> >> ... >>> >>> go wrong no correct substitution, in different ways >> >> then you write: >> >>> Interestingly until now I was simplifying correctly using >>> >>> my_ex.subs((*ddq_i)==0) > > You can disregard this sentence. > >> So, once it goes wrong, then it goes well?!? Did you upgrade GiNaC to a >> newer version, maybe? > > Disregard the my_ex.subs((*ddq_i)==0) goes OK thing, > >> Anyway, could you, if possible, send a complete code example to explain your >> problem? It is hard to guess what the problem might be, otherwise. > > It's going to take some time to isolate, as I'm using a library that > I've build on top of GiNaC to generate the offending my, but I'll try > if I can reproduce it using plain GiNaC, writing and reading it back > in a plain > GiNaC program. > > In any case I suppose that the trivial simplifications > > my_ex.subs((*ddq_i)==0) > > my_ex.subs(*ddq_i==0) > > my_ex.subs(symbol(*ddq_i)==0) > > should coincident with these > > my_ex.subs(lst(symbol(*ddq_i)==0,*ddq_i==0)) > > my_ex.subs(lst(symbol(*ddq_i)==0,(*ddq_i)==0)) > > But unfortunately only the last two are working. > > Do you agree that this is not normal behavior?. > > Thank you, > > Javier >

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Weird: symbol * ddq_i, my_ex.subs((*ddq_i)==0) my_ex.subs(*ddq_i==0) my_ex.subs(symbol(*ddq_i)==0) ??
by Javier Ros 27 Jul '11

27 Jul '11

Hello, Being symbol * ddq_i the following trivial simplifications my_ex.subs((*ddq_i)==0) my_ex.subs(*ddq_i==0) my_ex.subs(symbol(*ddq_i)==0) go wrong no correct substitution, in different ways but my_ex.subs(lst(symbol(*ddq_i)==0,*ddq_i==0)) and my_ex.subs(lst(symbol(*ddq_i)==0,(*ddq_i)==0)) go OK. Interestingly until now I was simplifying correctly using my_ex.subs((*ddq_i)==0) I think this is not correct behavior. What's your opinion?. I suppose that my current expresion is more complex than it used to be, that's why. I have not experienced this before. I'm using Ubuntu 10.04 LTS provided GiNaC, Synaptic tells 1.5.5 -1. Thank you, Javier

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problem parsing "{"
by Jan Piclum 26 Jul '11

26 Jul '11

Hi, I have a problem when I try to create expressions containing harmonic polylogarithms from strings. The example program (based on section 5.15.2 of the tutorial) #include <ginac/ginac.h> int main() { GiNaC::symbol x; GiNaC::symtab table; table["x"] = x; GiNaC::parser reader(table); GiNaC::ex e = reader("H({0},x)"); std::cout << e << std::endl; } terminates with the message terminate called after throwing an instance of 'GiNaC::parse_error' what(): GiNaC: parse error at line 0, column 0: unexpected token, got: "{" [GiNaC::ex GiNaC::parser::parse_primary()(parser/parser.cpp:161)] However, using the H({0},x) in ginsh works fine. I am using GiNaC version 1.6.1 on a 32bit Linux PC running openSUSE 11.3. The program was compiled with g++ version 4.5.0. Is this a bug or is this syntax for lists no longer supported? Thanks for your help. Best regards, Jan Piclum.

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Bug Report
by Jon Graves 22 Jul '11

22 Jul '11

OS: Ubuntu 11.04 Compiled with g++: g++ -o test test.cpp -lcln -lginac GiNaC ver: 1.60 Sample version of program attached. My program is only meant to simplify expressions that resemble this form: (x^n)^(1/n) = x This program is using a particular value of n to demonstrate what I believe to be a bug (n=2). Two similar methods are employed to attempt to simplify the expression, using wildcards, but only the first one works, while the second doesn't. The second one is the most general one, useful for any situation ... if it worked. Is this a bug? ~Jon

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Bug Report
by Jon Graves 20 Jul '11

20 Jul '11

OS: Ubuntu 11.04 Compiled with g++: g++ -o test test.cpp -lcln -lginac GiNaC ver: 1.60 Sample version of program attached. Program generates Hermite polynomial to high degree. It then subs into it a series of numbers. The output RANDOMLY generates an incorrect answer. No answer after a substitution should ever be zero, yet zeros inevitably appear. The problem occurs once out of every 3 executions, on average.

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Release 1.6.1
by Jens Vollinga 18 Jul '11

18 Jul '11

Hi everybody, GiNaC 1.6.1 is out and available. The changes are the following: * Fixed several internal assertions for the debug version of GiNaC. * More verbose report of (auto-)configuration problems. * Fixed a compile problem with ginsh using gcc 4.6. As always, this release can be downloaded from http://www.ginac.de/Download.html Regards, Jens

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3 index tensors
by Gregory Stiesberg 09 Jul '11

09 Jul '11

Hello, Given a matrix of expressions A and vectors q,v,w, I'm trying to evaluate a tensor expression of the type diff(A_ij, q_k) * v_k * w_j . With i,j,k of type idx, and A,q of type Matrix, It would be nice to get a 3 index tensor from indexed( diff(A(i,j),q(k)), i,j,k) or by diff(indexed(A,i,j),indexed(q,k)) but these don't work. After looking at the definition of epsilon_tensor the simplest option seems to be to write a class indexed_from_function3 able to return a 3-index tensor from an arbitrary function of three indices: for example ex f(int i, int j, int k){ return( diff(A(i,j),q(k)) ); } ex tensexp0=indexed_from_function3(f, i,j,k) * indexed(v, k) * indexed(w, j) Is there already a way to construct an arbitrary 3-index tensor that I've not found yet? Thanks in advance, Gregg Stiesberg

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Subresultant calculation
by Joachim Redies 07 Jul '11

07 Jul '11

Hello everbody, is it possible to calculate the subresultant of two multivariate polynomials (inherited from ex) with little development effort and knowledge about the mathematical background? I have seen that sr_gcd in normal.cpp uses subresultants. Is it possible to isolate the subresultant calulation? Thanks, Joachim

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Windows build
by Kraus Philipp 02 Jul '11

02 Jul '11

Hello, I would like to use Ginac under Windows (with Visual Studio). Is there a build script like cmake to build the Ginac library? I have build Ginac with cygwin but in my opinion I can't link again the cygwin binaries with VS, because the linker creates different calls, so if I use Ginac with VS I must create the binary with VS Thanks Phil

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