May 2019 - GiNaC-list

Re: [GiNaC-list] question about lorentz_g contract with sy_anti tensor
by Feng Feng 26 May '19

26 May '19

Thanks very much for your so quick reply. Yes, my mistake, I actually mean A^{abc}_{c} = A^{abcd} * g_{dc} So it goes back to my original post, it seems GiNaC will not produce a 0 result. Thanks again! Best Regards! Feng

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Re: [GiNaC-list] question about lorentz_g contract with sy_anti tensor
by Feng Feng 26 May '19

26 May '19

Tanks a lot! Yes and Sorry, I forgot to call simplified_indexed. Still, I get some confused with the index variance. and excuse me to let me explain my options in some details. I understand g_c^d = g_{ce} g^{ed}, and let’s come back to the ret expresion: "auto ret = indexed(A, sy_anti(0,1,2,3), ia,ib,ic,id) *lorentz_g(ic, id.toggle_variance());” In my understanding, it corresponds to A^{abcd} * g^{c}_{d}, is that right? if so, then A^{abcd} * g^{c}_{d} = A^{abcc}, so according to sy_anti, it is 0, directly from GiNaC. So if I want to contract two index in A, I mean, we need this one: A^{abc}_{c} = A^{abcd} * g^{dc} ? Thanks very much! Best Regards! Feng

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Re: [GiNaC-list] question about lorentz_g contract with sy_anti tensor
by Feng Feng 25 May '19

25 May '19

Thanks very for the reply. and I have tried the suggestion, i.e., using the following expression: auto ret = indexed(A, sy_anti(0,1,2,3), ia,ib,ic,id) * lorentz_g(ic, id.toggle_variance()); but I got something like: -delta.d~c*A~d~a~b~c, still a non-zero result. BTW, if c’s variance is not toggled in lorentz_g, then these two dummy index c’s variance is not matched, and is that allowed? Thanks again!

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question about lorentz_g contract with sy_anti tensor
by Feng Feng 23 May '19

23 May '19

Hi all, I wonder is there a way or method to simplify the expression with a sy_anti tensor contracted with a lorent_g to 0? Please have a look at the following code, I expect ret is 0, and the output looks like “A~b~a.c~c”, it is actually 0 due to the sy_anti, but I wonder, is there a way or a method to simplify those expression directly to 0? Thanks very much! using namespace GiNaC; using namespace std; int main(int argc, char** argv) { symbol a("a"), b("b"), c("c"), d("d"), A("A"); symbol D("D"); varidx ia(a,D), ib(b,D), ic(c,D), id(d,D); auto ret = indexed(A, sy_anti(0,1,2,3), ia,ib,ic,id) * lorentz_g(ic.toggle_variance(), id.toggle_variance()); cout << simplify_indexed(ret) << endl; return 0; } Best regards! Feng

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Crash with zeta({7, 3}), and performance difference with G(...)
by Vitaly Magerya 22 May '19

22 May '19

Hi, folks. I've run into a crash; here it is: (gdb) run Starting program: .../ginac/build/ginsh/ginsh ginsh - GiNaC Interactive Shell (GiNaC V1.7.6) __, _______ Copyright (C) 1999-2019 Johannes Gutenberg University Mainz, (__) * | Germany. This is free software with ABSOLUTELY NO WARRANTY. ._) i N a C | You are welcome to redistribute it under certain conditions. <-------------' For details type `warranty;'. Type ?? for a list of help topics. > evalf(zeta({7,3})); 0.008419668503096332361 > Digits=2000; 2000 > evalf(zeta({7,3})); Program received signal SIGSEGV, Segmentation fault. 0x00007ffff786c3ca in cln::operator*(cln::cl_N const&, cln::cl_N const&) () from /usr/lib/libcln.so.6 (gdb) bt #0 0x00007ffff786c3ca in cln::operator*(cln::cl_N const&, cln::cl_N const&) () from /usr/lib/libcln.so.6 #1 0x00005555556402c1 in GiNaC::(anonymous namespace)::crandall_Y_loop(cln::cl_N const&, std::vector<cln::cl_N, std::allocator<cln::cl_N> > const&) () #2 0x0000555555658ab9 in GiNaC::zeta1_evalf(GiNaC::ex const&) () #3 0x00005555555f5697 in GiNaC::function::evalf() const () #4 0x0000555555586023 in f_evalf(GiNaC::container<std::vector> const&) () #5 0x000055555558d7c7 in yyparse() () #6 0x0000555555577087 in main () (gdb) Interestingly evaluating the same zeta with G works fine: > Digits=2000; 2000 > evalf(G({0,0,0,0,0,0,1,0,0,1},1)); 0.00841966850309633242396857971467065063691... Also with Digits=500, evaluating zeta({7,3}) takes ~10 seconds, while it's only 0.6 seconds for G({0,0,0,0,0,0,1,0,0,1},1). Anyone has ideas as to why is there such difference in performance, and is there an even faster way?

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casting
by Pedro Sosa 07 May '19

07 May '19

Hello, I'm a begginer and I don't find how to convert from ex to double in the tutorialSomebody can help me? Thanks

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Different Compiling Command
by Hanni Puspita 01 May '19

01 May '19

Hello, I am new to GiNaC and I follow a pdf doc tutorial that documents GiNaC 1.7.6 for installation and testing. However there is a inconsistency that I found in the pdf doc on how to compile the scripts. Not working : G++ HELLO.CPP -O HELLO -LCLN -LGINAC Works : G++ HELLO.CPP -O HELLO -LGINAC -LCLN Perhaps you should update the tutorial docs? I use Windows 10 and GCC 7.4.0. Thanks. Best regards, Hanni Puspita

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