[GiNaC-devel] Performance Problem with subs

[Frieder Kalisch]

Hello,

there is something severely wrong performance wise with subs and or eval in 
ginac. Suppose I want to expand 1/(a+sqrt(b*b+x*x)) in a power series in x 
around x==1 and then substitute numerical values (floating point) for a, b 
and x.

Doing this straight forwardly with series(), series_to_poly() and subs() 
[program 1] needs 0.01 seconds for series and series_to_poly and 15.99 
seconds for subs. However, if I define my own functions f1(x)->1/x and f2
(x)->sqrt(x) using DECLARE_FUNCTION_1P and REGISTER_FUNCTION with the only 
function options being evalf_func and derivative_func [program 2], it takes 
0.09 seconds to do series() and series_to_poly() and 0.02 seconds for the 
subs()!

I suspect, that ginac somehow tries to restructure the expression on a large 
scale, since if I insert an expand() in the first case between 
series_to_poly() and subs() [program 3], it takes 15.99 seconds to do the 
expand() and only 0.12 seconds for the subs().

I have used ginac-version 1.2.4-1 on debian sarge. Attached to this Email You 
find the source code for my program. Please ask if You have any questions.

Regards

           Frieder Kalisch

-- 
Frieder Kalisch                         Institut für theoretische Physik
kalisch at tphys.uni-heidelberg.de         Philosophenweg 19
+49-6221-549-433                        D-69120 Heidelberg

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