Re: 1-0.95

2014-07-03 Thread Marko Rauhamaa
Steven D'Aprano : > If you don't think Fraction counts as "arbitrary precision rational > number", what do you think does? I was assuming you were referring to an idealized datatype. Fraction() doesn't have a square root method. Let's make one: def newton(x, n): guess = Fraction(1)

Re: 1-0.95

2014-07-03 Thread Steven D'Aprano
On Thu, 03 Jul 2014 09:51:35 +0300, Marko Rauhamaa wrote: > Steven D'Aprano : [...] >> By the way, there's no need to use an invented example. Here is an >> actual example: >> >> py> import math >> py> from fractions import Fraction >> py> math.sqrt(Fraction(2))**2 >> 2.0004 > > Sure,

OT: speeds (physical, not computing) [was Re: 1-0.95]

2014-07-03 Thread Steven D'Aprano
On Wed, 02 Jul 2014 21:06:52 -0700, Rustom Mody wrote: > On Thursday, July 3, 2014 7:49:30 AM UTC+5:30, Steven D'Aprano wrote: >> On Wed, 02 Jul 2014 23:00:15 +0300, Marko Rauhamaa wrote: > >> > On the other hand, floating-point numbers are perfect whenever you >> > deal with science and measurem

Re: 1-0.95

2014-07-02 Thread Marko Rauhamaa
Steven D'Aprano : > On Wed, 02 Jul 2014 23:00:15 +0300, Marko Rauhamaa wrote: >> Steven D'Aprano : >>> Rational(2).sqrt() * Rational(2).sqrt() == Rational(2) False >>> Square root of 2 is not a rational number. >> Nobody said it was. > > Your comment can be read as implying it. Yo

Re: 1-0.95

2014-07-02 Thread Ian Kelly
On Wed, Jul 2, 2014 at 10:55 PM, Gregory Ewing wrote: > Although loss of precision might give you the > right answer anyway. :-) There aren't that many digits in the speed of light. Unless we're talking about a very, very slow-moving automobile. -- https://mail.python.org/mailman/listinfo/pytho

Re: 1-0.95

2014-07-02 Thread Rustom Mody
On Thursday, July 3, 2014 10:25:17 AM UTC+5:30, Gregory Ewing wrote: > Rustom Mody wrote: > > Just as there are even some esteemed members of this list who think > > that c - a is a meaningful operation > > where > > c is speed of light > > a is speed of an automobile > Indeed, it should

Re: 1-0.95

2014-07-02 Thread Gregory Ewing
Rustom Mody wrote: Just as there are even some esteemed members of this list who think that c - a is a meaningful operation where c is speed of light a is speed of an automobile Indeed, it should be (c - a) / (1 - (c*a)/c**2). Although loss of precision might give you the right answer

Re: 1-0.95

2014-07-02 Thread Rustom Mody
On Thursday, July 3, 2014 7:49:30 AM UTC+5:30, Steven D'Aprano wrote: > On Wed, 02 Jul 2014 23:00:15 +0300, Marko Rauhamaa wrote: > > On the other hand, floating-point numbers are perfect whenever you deal > > with science and measurement. > /head-desk Just as there are even some esteemed mem

Re: 1-0.95

2014-07-02 Thread Steven D'Aprano
On Wed, 02 Jul 2014 23:00:15 +0300, Marko Rauhamaa wrote: > Steven D'Aprano : > >>>>>> Rational(2).sqrt() * Rational(2).sqrt() == Rational(2) >>>False >> >> Square root of 2 is not a rational number. > > Nobody said it was. Your comment can be read as implying it. You stated: [quo

Re: 1-0.95

2014-07-02 Thread Chris Angelico
On Thu, Jul 3, 2014 at 6:00 AM, Marko Rauhamaa wrote: > Steven D'Aprano : > >>>>>> Rational(2).sqrt() * Rational(2).sqrt() == Rational(2) >>>False >> >> Square root of 2 is not a rational number. > > Nobody said it was. It's just that even "arbitrary-precision" rational > numbers wouldn't

Re: 1-0.95

2014-07-02 Thread Marko Rauhamaa
Steven D'Aprano : >>>>> Rational(2).sqrt() * Rational(2).sqrt() == Rational(2) >>False > > Square root of 2 is not a rational number. Nobody said it was. It's just that even "arbitrary-precision" rational numbers wouldn't free you from the issues of floating-point numbers. The Decimal num

Re: 1-0.95

2014-07-02 Thread Steven D'Aprano
On Wed, 02 Jul 2014 19:59:25 +0300, Marko Rauhamaa wrote: > Steven D'Aprano : > >> This is a problem with the underlying C double floating point format. >> Actually, it is not even a problem with the C format, since this >> problem applies to ANY floating point format, consequently this sort of >

Re: 1-0.95

2014-07-02 Thread Skip Montanaro
On Wed, Jul 2, 2014 at 11:59 AM, Marko Rauhamaa wrote: > Yes, I'm making it up, but it's still true. I don't think there's any reason to be hypothetical: In [149]: d Out[149]: Decimal('2') In [150]: d.sqrt() * d.sqrt() == d Out[150]: False :-) Skip -- https://mail.python.org/mailman/listinfo

Re: 1-0.95

2014-07-02 Thread Marko Rauhamaa
Steven D'Aprano : > This is a problem with the underlying C double floating point format. > Actually, it is not even a problem with the C format, since this > problem applies to ANY floating point format, consequently this sort > of thing plagues *every* programming language (unless they use > arb

Re: 1-0.95

2014-07-02 Thread Steven D'Aprano
On Tue, 01 Jul 2014 14:17:14 -0700, Pedro Izecksohn wrote: > pedro@microboard:~$ /usr/bin/python3 > Python 3.3.2+ (default, Feb 28 2014, 00:52:16) [GCC 4.8.1] on linux > Type "help", "copyright", "credits" or "license" for more information. >&

Re: 1-0.95

2014-07-01 Thread pecore
Pedro Izecksohn writes: > pedro@microboard:~$ /usr/bin/python3 > Python 3.3.2+ (default, Feb 28 2014, 00:52:16) > [GCC 4.8.1] on linux > Type "help", "copyright", "credits" or "license" for more information. >>>> 1-0.95 > 0.0500

Re: 1-0.95

2014-07-01 Thread Mark Lawrence
On 01/07/2014 22:17, Pedro Izecksohn wrote: pedro@microboard:~$ /usr/bin/python3 Python 3.3.2+ (default, Feb 28 2014, 00:52:16) [GCC 4.8.1] on linux Type "help", "copyright", "credits" or "license" for more information. 1-0.95 0.050044

1-0.95

2014-07-01 Thread Pedro Izecksohn
pedro@microboard:~$ /usr/bin/python3 Python 3.3.2+ (default, Feb 28 2014, 00:52:16) [GCC 4.8.1] on linux Type "help", "copyright", "credits" or "license" for more information. >>> 1-0.95 0.050044 >>>    How to get 0.05 as r