On Nov 30 08:38:27, p...@delphinusdns.org wrote: > In fact it's not just bc -l, but also when I calculate the following in C > (linked with -lm) > > C = (180.0 - A) - B; > a = (double)(c / sin(C)) * sin(A); > b = (double)(c / sin(C)) * sin(B); > > Some may recognize this as parts of the Law of Sines. > > pjp@neptune$ bc -l > (9 / s(70)) * s(76) > 6.58357679385302895866 > > When I do it with xcalc I get the correct 9.2931043.
Look at /usr/share/misc/bc.library to see what bc's s(x) really is. Then look at lib/libm/ to see what sin() and friends really are. (Yes, a Taylor polynom around zero; almost.) It is known that the values of goniometric functions can get way off: sin() at multiples of pi is nonzero, etc. For extra laughs, read this article https://randomascii.wordpress.com/2014/10/09/intel-underestimates-error-bounds-by-1-3-quintillion/ about how Intel tried to have fsin() in their instruction set. Jan
