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Re: Code style query: multiple assignments in if/elif tree

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On Tue, Apr 1, 2014 at 1:35 AM, Chris Angelico <rosuav@gmail.com> wrote:
> On Tue, Apr 1, 2014 at 6:20 PM, Steven D'Aprano <steve@pearwood.info> wrote:
>> 177.211111333333
>>
>> compared to 177.26527800000002 calculated the rough way. That's not bad,
>> only about 5cm off! Effectively, your rough calculation was accurate to
>> one decimal place.
>
> 5cm when we're dealing with track distances measured in meters and
> usually hundreds of them? Sounds fine to me!

Erm, that's just the accumulated error over the first 2 seconds,
though.  A train moving at 88 m/s and decelerating at a maximum of
0.85 m/s^2 is not going to stop in just 177 meters.

After the first 2 seconds, the model is the same using either method,
but the velocity after 2 seconds is different.  Using the linear
deceleration integration, we get:

a(t) = {-0.425t, t <= 2;
        -0.85, t > 2}
v(t) = {v0 - 0.2125t^2, t <= 2;
        v0 - 0.85 - 0.85t, t > 2}

Giving v(2s) = v0 - 0.85 m/s

Using the averaging method, we get v(2s) = v0 - 0.2 - 0.425 = v0 - 0.625 m/s

For a difference of 0.225 m/s.  Using Steven's formula (4), the
additional difference in stopping distance is thus:

Δs = ((0 - (88.888889 - 0.625)^2) - (0 - (88.888889 - 0.85)^2)) / -1.7
     = 23.33 m

The reason the velocity is different after 2 seconds is because the
linear deceleration does not match the constraints of the problem. The
average deceleration for the first second is not 0.2 m/s, and the
average deceleration for the second second is not 0.425 m/s.

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Code style query: multiple assignments in if/elif tree Chris Angelico <rosuav@gmail.com> - 2014-04-01 01:33 +1100
  Re: Code style query: multiple assignments in if/elif tree Marko Rauhamaa <marko@pacujo.net> - 2014-03-31 18:40 +0300
    Re: Code style query: multiple assignments in if/elif tree Chris Angelico <rosuav@gmail.com> - 2014-04-01 03:03 +1100
      Re: Code style query: multiple assignments in if/elif tree Rustom Mody <rustompmody@gmail.com> - 2014-03-31 09:20 -0700
        Re: Code style query: multiple assignments in if/elif tree Chris Angelico <rosuav@gmail.com> - 2014-04-01 03:29 +1100
          Re: Code style query: multiple assignments in if/elif tree "Rhodri James" <rhodri@wildebst.org.uk> - 2014-03-31 21:31 +0100
    Re: Code style query: multiple assignments in if/elif tree Ned Batchelder <ned@nedbatchelder.com> - 2014-03-31 17:42 -0400
    Re: Code style query: multiple assignments in if/elif tree Chris Angelico <rosuav@gmail.com> - 2014-04-01 09:50 +1100
    Re: Code style query: multiple assignments in if/elif tree Ben Finney <ben+python@benfinney.id.au> - 2014-04-01 09:57 +1100
    Re: Code style query: multiple assignments in if/elif tree Chris Angelico <rosuav@gmail.com> - 2014-04-01 10:12 +1100
      Re: Code style query: multiple assignments in if/elif tree Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-04-01 00:57 +0000
    Re: Code style query: multiple assignments in if/elif tree Ethan Furman <ethan@stoneleaf.us> - 2014-03-31 17:30 -0700
  Re: Code style query: multiple assignments in if/elif tree Steven D'Aprano <steve@pearwood.info> - 2014-04-01 04:26 +0000
    Re: Code style query: multiple assignments in if/elif tree Chris Angelico <rosuav@gmail.com> - 2014-04-01 16:01 +1100
      Re: Code style query: multiple assignments in if/elif tree Steven D'Aprano <steve@pearwood.info> - 2014-04-01 07:20 +0000
        Re: Code style query: multiple assignments in if/elif tree Chris Angelico <rosuav@gmail.com> - 2014-04-01 18:35 +1100
          Re: Code style query: multiple assignments in if/elif tree Steven D'Aprano <steve@pearwood.info> - 2014-04-01 08:07 +0000
            Re: Code style query: multiple assignments in if/elif tree Chris Angelico <rosuav@gmail.com> - 2014-04-01 19:12 +1100
        Re: Code style query: multiple assignments in if/elif tree Ian Kelly <ian.g.kelly@gmail.com> - 2014-04-01 02:18 -0600
        Re: Code style query: multiple assignments in if/elif tree Ian Kelly <ian.g.kelly@gmail.com> - 2014-04-01 02:24 -0600
    Re: Code style query: multiple assignments in if/elif tree Rustom Mody <rustompmody@gmail.com> - 2014-03-31 22:45 -0700
      Re: Code style query: multiple assignments in if/elif tree David Hutto <dwightdhutto@gmail.com> - 2014-04-01 02:05 -0400
      Re: Code style query: multiple assignments in if/elif tree Ian Kelly <ian.g.kelly@gmail.com> - 2014-04-01 00:28 -0600
    Re: Code style query: multiple assignments in if/elif tree Ian Kelly <ian.g.kelly@gmail.com> - 2014-04-01 00:13 -0600
    Re: Code style query: multiple assignments in if/elif tree David Hutto <dwightdhutto@gmail.com> - 2014-04-01 02:24 -0400
    Re: Code style query: multiple assignments in if/elif tree Ian Kelly <ian.g.kelly@gmail.com> - 2014-04-01 00:39 -0600
    Re: Code style query: multiple assignments in if/elif tree Chris Angelico <rosuav@gmail.com> - 2014-04-01 17:55 +1100
      Re: Code style query: multiple assignments in if/elif tree Steven D'Aprano <steve@pearwood.info> - 2014-04-01 07:29 +0000
        Re: Code style query: multiple assignments in if/elif tree Chris Angelico <rosuav@gmail.com> - 2014-04-01 18:49 +1100
        Re: Code style query: multiple assignments in if/elif tree Ian Kelly <ian.g.kelly@gmail.com> - 2014-04-01 02:29 -0600
        Re: Code style query: multiple assignments in if/elif tree Chris Angelico <rosuav@gmail.com> - 2014-04-01 19:56 +1100
    Re: Code style query: multiple assignments in if/elif tree David Hutto <dwightdhutto@gmail.com> - 2014-04-01 03:21 -0400
    Re: Code style query: multiple assignments in if/elif tree Chris Angelico <rosuav@gmail.com> - 2014-04-01 18:26 +1100
    Re: Code style query: multiple assignments in if/elif tree David Hutto <dwightdhutto@gmail.com> - 2014-04-01 03:34 -0400
    Re: Code style query: multiple assignments in if/elif tree David Hutto <dwightdhutto@gmail.com> - 2014-04-01 03:39 -0400
    Re: Code style query: multiple assignments in if/elif tree David Hutto <dwightdhutto@gmail.com> - 2014-04-01 03:46 -0400
    Re: Code style query: multiple assignments in if/elif tree Ian Kelly <ian.g.kelly@gmail.com> - 2014-04-01 02:55 -0600

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