Re: What Floating-Point Precisions Would Physicists Prefer?

From	Poutnik <Poutnik4NNTP@gmail.com>
Newsgroups	sci.physics
Subject	Re: What Floating-Point Precisions Would Physicists Prefer?
Date	2015-08-05 14:36 +0200
Organization	Good company
Message-ID	<mpsvso$gai$1@dont-email.me> (permalink)
References	<05569dcb-68b3-4154-8bab-f13fd12a379a@googlegroups.com> <c567212e-4567-4752-b118-6bb6eadfb87e@googlegroups.com>

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On 08/05/2015 01:47 PM, Timo wrote:
> On Wednesday, August 5, 2015 at 1:43:24 PM UTC+10, Quadibloc wrote:
>>
>> Also, there is a lot of historical evidence - from scientific pocket 
>> calculators going all the way back to logarithm tables - that ten digits was 
>> viewed as the appropriate precision to reach for when high accuracy was needed.
>>
>> This would mesh well with a 48-bit floating point format, which can give eleven 
>> digits of precision.
> 
> Assuming you start with 11 digits of precision, how many correct digits are you left with after calculating a derivative numerically?
> 
> If you're going to do that kind of thing, better to start with double precision, and have those extra digits available to lose.
> 
>> Are there sources of informatiion on how much precision is needed for various 
>> types of scientific computation?
> 
> Practical experience says that, most of the time, double precision is enough. Can lose half the precision, and still have an accurate result. Can lose half the precision twice, and still have an adequate result.
> 
> I like a correct digit or two more than the experimental results I'll be comparing my calculations to. I won't complain about more correct digits than that, but that's enough.
> 
Physics itself IMHO usually need not high precission,
but underlying numeracal math procedures often do.

Especially  if many iterations with error propagation are involved,
like  numerical solution of differencial equations
with particular border/initial conditions.

Also if math nature of the equation is being dynamically unstable,
like Richardson's partial differential equation for athmosphere
evolvement, or equations describing fluid turbulence.

-- 
Poutnik ( the Czech word for a wanderer )

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What Floating-Point Precisions Would Physicists Prefer? Quadibloc <jsavard@ecn.ab.ca> - 2015-08-04 20:41 -0700
  Re: What Floating-Point Precisions Would Physicists Prefer? Fabian Russell <root@localhost.localdomain> - 2015-08-05 05:14 +0000
    Re: What Floating-Point Precisions Would Physicists Prefer? Quadibloc <jsavard@ecn.ab.ca> - 2015-08-05 04:38 -0700
      Re: What Floating-Point Precisions Would Physicists Prefer? Fabian Russell <root@localhost.localdomain> - 2015-08-05 14:22 +0000
        nano-M-sets noTthaTguY <abu.kuanysh05@gmail.com> - 2015-08-05 13:14 -0700
          Re: nano-M-sets Fabian Russell <root@localhost.localdomain> - 2015-08-05 21:23 +0000
            Re: nano-M-sets Poutnik <poutnik4nntp@gmail.com> - 2015-08-06 08:16 +0200
              Re: nano-M-sets Fabian Russell <root@localhost.localdomain> - 2015-08-06 17:34 +0000
                Re: nano-M-sets Quadibloc <jsavard@ecn.ab.ca> - 2015-08-06 11:23 -0700
                Re: nano-M-sets Fabian Russell <root@localhost.localdomain> - 2015-08-06 18:39 +0000
                Re: nano-M-sets Poutnik <poutnik4nntp@gmail.com> - 2015-08-06 21:07 +0200
                Re: nano-M-sets Fabian Russell <root@localhost.localdomain> - 2015-08-06 19:14 +0000
                Re: nano-M-sets Poutnik <poutnik4nntp@gmail.com> - 2015-08-07 07:41 +0200
                Re: nano-M-sets Quadibloc <jsavard@ecn.ab.ca> - 2015-08-06 14:17 -0700
                Re: nano-M-sets Fabian Russell <root@localhost.localdomain> - 2015-08-06 21:36 +0000
                Re: nano-M-sets Poutnik <poutnik4nntp@gmail.com> - 2015-08-07 08:08 +0200
                Re: nano-M-sets Poutnik <poutnik4nntp@gmail.com> - 2015-08-06 21:05 +0200
        Re: What Floating-Point Precisions Would Physicists Prefer? Quadibloc <jsavard@ecn.ab.ca> - 2015-08-06 11:18 -0700
          Re: What Floating-Point Precisions Would Physicists Prefer? Fabian Russell <root@localhost.localdomain> - 2015-08-06 19:03 +0000
            Re: What Floating-Point Precisions Would Physicists Prefer? Quadibloc <jsavard@ecn.ab.ca> - 2015-08-06 14:11 -0700
              Re: What Floating-Point Precisions Would Physicists Prefer? Fabian Russell <root@localhost.localdomain> - 2015-08-06 21:51 +0000
                Re: What Floating-Point Precisions Would Physicists Prefer? Quadibloc <jsavard@ecn.ab.ca> - 2015-08-06 15:18 -0700
                Re: What Floating-Point Precisions Would Physicists Prefer? Fabian Russell <root@localhost.localdomain> - 2015-08-07 01:11 +0000
                Re: What Floating-Point Precisions Would Physicists Prefer? noTthaTguY <abu.kuanysh05@gmail.com> - 2015-08-07 10:25 -0700
                Re: What Floating-Point Precisions Would Physicists Prefer? Quadibloc <jsavard@ecn.ab.ca> - 2015-08-07 11:41 -0700
                Re: What Floating-Point Precisions Would Physicists Prefer? "hanson" <hanson@quick.net> - 2015-08-07 16:21 -0700
  Re: What Floating-Point Precisions Would Physicists Prefer? Timo <timo@physics.uq.edu.au> - 2015-08-05 04:47 -0700
    Re: What Floating-Point Precisions Would Physicists Prefer? Poutnik <Poutnik4NNTP@gmail.com> - 2015-08-05 14:36 +0200

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