Hi, On Mon, 10 Mar 2003, Ola Skavhaug wrote:
I think I've encountered a bug in GiNaC-1.0.13 (on a Debian Linux machine) In ginsh:
diff(sqrt((-sin((x)))^(2.0)),x); (1.0+5.0165576136843360246E-20*I)*sin(x)*cos(x)*((-sin(x))^(2.0))^(-1/2)
The answer should be: sin(x)*cos(x)*((-sin(x))^(2.0))^(-1/2)
I have not tried to figure out why this happens (perhaps an uninitialized variable?) I've compiled ginac by myself, using cln-1.1.5 (gcc 3.2 compiler)
I haven't any idea why you think this is due to an uninitialized variable, but, well, it isn't a bug, strictly speaking. Such behavior is to be expected when dealing with floating points. You should use an integer exponent. In your example (or the slightly simpler diff(sqrt((-x)^(2.)),x)), some stages after power::diff() a mul::combine_overall_coeff(ex, ex) happens, and therin numeric::power() is being called, which in turn calls cln::expt(-1,1.0). That is not guaranteed to be equal -1 by CLTL. However, I do think that we should be somewhat more careful trying to check for unit exponents, but for another reason: When numeric::power_dyn() returns a reference, it can return a pointer to an *existing* object instead of creating a new one on the heap. This will account for some more comparisons by pointer later on and hence be a performance win. For reasons of symmetry, the same check should be done in numeric::power(). I have committed such a patch to the 1.1 and the 1.2 branches. But surprises are still gonna happen with floating point examples unless we start using BCD which I'm sure you don't want. ;-) Cheers -richy. -- Richard B. Kreckel <Richard.Kreckel@GiNaC.DE> <http://www.ginac.de/~kreckel/>