On Dec 15, 2008, at 5:04 PM, Javier Ángel Velázquez Muriel wrote:
No hardcoded tolerance will work reliably as the error varies tremendously depending on the calculation or whether you are just worrying about 80 bit to 32 bit conversion error. And I think users should be kept aware of this, so the error should be user specified.2008/12/15 <>:I am currently using the class vector3D derived from vectorD and I have noticed that the compare function is very strict. That is, when checking if a vector is zero, and is for example (0,0,0.00001), I would probably like that the function returns yes. Same thing with other vectors, and matrices, and everything that can vary whit rounding errors. I propose (In fact I have done it already but not submitted it to SVN) to have a math_macros.h file that defines this kind of things and specifically here define the macro EQUALITY_TOLERANCE. I have put a value 1e-6 to it, but maybe you have different opinions, guys.
What I tend to do is do (a-b).get_squared_magnitude() < tolerance. which is reasonably concise compared to a macro and expresses directly what we are evaluating. That said, it might make sense to have functions which evaluate other metrics on vectors, such as l_infinity norm.
The comparison functions are just there for inserting them into maps and other storage methods as they aren't particularly useful in general. I tend to like to make sure that things can be put into std::sets, but the comparisons are not used at the moment, and perhaps should be removed.