> > > @Jan The fact that two floats are converted to the same string with "print" does > not imply that they are equal. Before printing a number, python is rounding > and truncating. >
sorry, you are right, [1] shows that decimal representation is indeed rounded.. > Real number representation is still a mystery to me, I know just enough to > know that it is never as simple as one expects. > For instance, this is not a bug: > >>> x=0.1; y=0.2 > >>> x+y > 0.30000000000000004 > >>> print x+y > 0.3 > see Vaclav's thesis, section 2.7.2 or [1] > > This being said, your conclusion may be right (I'm still not 100% sure) > even though the proof was flawn, since a variant of your script with "all" > digits displayed gives this: > 0.2017354310946590789654919717577286064624786376953125 > 0.2017354310946590789654919717577286064624786376953125 > 0.2017354310946590789654919717577286064624786376953125 > 0.2017354310946590789654919717577286064624786376953125 > see [1] (again :-) > ___ > import random; r=random.random > from decimal import Decimal #see > https://docs.python.org/2/tutorial/floatingpoint.html > O.bodies.append(sphere((r(),r(),r()),1)) > base = '/tmp/a.' > for ext in 'yade','xml': > print Decimal(O.bodies[0].state.pos[0]) > O.save(base+ext) > O.reset() > O.load(base+ext) > print Decimal(O.bodies[0].state.pos[0]) > > Another (and it seems to me that really proving) alternative is to use Python float.hex() function [2], that prints what is really in the memory: ... print O.bodies[0].state.pos[0].hex() cheers Jan > [1] https://docs.python.org/2/tutorial/floatingpoint.html [2] https://docs.python.org/2/library/stdtypes.html#float.hex
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