On Fri, 2006-11-17 at 16:51 -0500, Michael B. Trausch wrote: > On Fri, 2006-11-17 at 21:25 +0100, Fredrik Lundh wrote: > > > Some of the lat/long pairs that I have used seem to come out fine, but > > > some do not. Because the mathmatics used with them involve complex > > > equations when determining distance and the like, any error gets > > > massively compounded before a final result is evident. > > > > sorry, but I don't think you have the slightest idea what you're doing, > > really. > > > > Sure, I do. Let's say that I want to work with the latitude > 33.6907570. In Python, that number can not be stored exactly without > the aid of decimal.Decimal(). > > >>> 33.6907570 > 33.690756999999998 > >>> > > As you can see, it loses accuracy after the 6th decimal place. That's > not good enough: I have 8 numbers that need to be exact, and I am > only getting six.
Really? >>> x = 33.6907570 >>> for i in range(7,16): print "%.*f" % (i,x) ... 33.6907570 33.69075700 33.690757000 33.6907570000 33.69075700000 33.690757000000 33.6907570000000 33.69075700000000 33.690756999999998 Looks to me like you're getting, uh, 14 decimal digits, for a total of 16 significant digits. What kinds of operations are you performing that compound this error by seven orders of magnitude? -Carsten -- http://mail.python.org/mailman/listinfo/python-list
