September 2005 - GiNaC-devel

Patch for products of dummy summations
by Vladimir Kisil 12 Nov '05

12 Nov '05

Here is the patch which was described in my previous message (Fri May 13 17:27:25 CEST 2005). -- Vladimir V. Kisil email: kisilv(a)maths.leeds.ac.uk -- www: http://maths.leeds.ac.uk/~kisilv/

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patch for simplify_indexed.
by Chris Dams 01 Oct '05

01 Oct '05

Dear developers, When simplify_indexed() is called two symmetrizations w.r.t dummy indices are performed. In these two cases symmetrization w.r.t. all dummy indices is done. However, it is also possible to do symmetrization with respect to ordinary idx-es, varidx-es and spinidx-es seperately. The latter is potentially much faster. E.g. Today I had an example where some terms contained 5 ordinary dummy indices and 2 dummy indices with variance. In this case a factor of 21 fewer terms are generated by the latter option. (I.e. 7!/5!/2!=21). Therefore symmetrizing seperately can be much faster. A patch is attached. Best wishes, Chris

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Function & Power patch
by Vladimir Kisil 26 Sep '05

26 Sep '05

Dear All, There are many functions (abs, Heaviside, exp) which possess some power-simplification rules. I propose a patch to power.cpp and function.pl which allows to defines such rules in a way similar to derivative rules of functions. With the help of this I slightly improve the definition of abs() and it work now in this way: #include <ginac/ginac.h> using namespace GiNaC; int main(){ realsymbol a("a"); cout << pow(abs(a), 2) << endl; // -> a^2 cout << pow(abs(a), 3) << endl; // -> abs(a)^3 symbol r("r"); cout << pow(abs(r), 2) << endl; // -> abs(r)^2 cout << pow(abs(r), 3) << endl; // -> abs(r)^3 } i.e. pow(abs(a), 2*n) is simplified to pow(a, 2*n) for real a. I also delete a duplicated line from ginac.texi. If it will be useful to add a definition of Heaviside function to the GiNaC core, I can send a patch as well. Best wishes, Vladimir -- Vladimir V. Kisil email: kisilv(a)maths.leeds.ac.uk -- www: http://maths.leeds.ac.uk/~kisilv/

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Patch for adaptivesimpson.
by Chris Dams 15 Sep '05

15 Sep '05

Dear developers, Could you apply the attached patch to integral.cpp? It adds some checks to adaptivesimpson to see whether the boundaries of integration and the integration error really are numbers and, as discussed with Richy, it makes the lookup table take into account that adaptivesimpson may be called with the same integral but different precision. Best wishes, Chris

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Numerical integration in GiNaC
by Richard B. Kreckel 13 Sep '05

13 Sep '05

Hi Chris! I was playing with the adaptive Simpson function and found some problems evaluating numerically a (well-behaved) integral. I've a couple of questions: 1) Why the decision to *not* couple the precision to the value of Digits? Coupling it to Digits would make it available in Ginsh. Wouldn't it do the right thing in almost all cases? 2) Are variations of Simpson's rule really attractive for numerical evaluation? Have you considered/tried something funkier (maybe Romberg's method) or is that a particularly smart implementation? 3) Probably an oversight: the last argument to the adaptivesimpson function is unused. Instead, the code always uses the default. Best wishes -richy. -- Richard B. Kreckel <http://www.ginac.de/~kreckel/>

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patch for power::expand_mul
by Chris Dams 09 Sep '05

09 Sep '05

Dear developers, Could you change the line if (get_all_dummy_indices(m).size() > 0) { that occurs in the function power::expand_mul in power.cpp into if (get_all_dummy_indices(m).size() > 0 && n.is_positive()) { Reason: I sometimes use algebraic substitution for expressions involving indices. For instance using the pattern indexed(UL1inv,wildgen,wildgen2)*indexed(UL1,wildgen2,wildgen3) ==delta_tensor(wildgen,wildgen3) to cancel a matrix multiplied with its inverse. Internally, algebraic subsitution divides by the factors it wants to get rid of but since Vladimir Kisils patch this goes wrong if these factors contain a contraction. Best wishes, Chris

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