[ExI] ai class at stanford

Emlyn emlynoregan at gmail.com
Fri Aug 26 00:09:02 UTC 2011

On 26 August 2011 05:51, spike <spike66 at att.net> wrote:
>>... On Behalf Of Adrian Tymes
> Subject: Re: [ExI] ai class at stanford
> On Thu, Aug 25, 2011 at 2:50 AM, Emlyn <emlynoregan at gmail.com> wrote:
>>> Spreadsheets are fine for temporary/initial/interim solutions, but
>>> long term, they promote crazy spaghetti code, write-only code. It's
>>> un-analyzable, un-maintainable.
>>...Agreed.  Problem is, if you have a decade-plus of code in spreadsheets,
> it can be really hard (nearly impossible) to make the case to management
> that it's time to spend a lot of not-immediately-productive time porting it
> to something better - especially if, as in Spike's case, they are personally
> invested in the spreadsheets.
> _______________________________________________
> This all brings back pleasant memories from my misspent early career.  We
> had a pile of Fortran code which calculates rocket ascent trajectories,
> which I ported over to a spreadsheet because I found it easier to set up
> iterative studies, and also so I could run it at home.  That Fortran code is
> dead now, but the spreadsheet lives on.
> An early example from 1991 is this: assuming away the atmosphere, is the
> optimal rocket ascent a gravity turn?
> If you know what is a gravity turn, skip to the next paragraph.  A gravity
> turn is where you have a rocket set to blast into orbit from the surface of
> a planet which rotates west to east as the earth does.  It is tilted east as
> a slight angle from vertical, perhaps a milliradian, so that in the first
> time increment it rises but also tilts slightly more east, then the next
> increment slightly more, such that just as it attains orbit velocity it is
> flying horizontal.
> Answer: on an airless planet, the gravity turn is the optimal ascent.
> Closed form solutions are possible.
> OK, now assume an earthlike atmosphere, but perfectly still, no wind.  Is a
> gravity turn still optimal?  Answer: no.
> Can you prove it in closed form?  Answer: no, not on my best day in my
> fondest dream.
> Can you show it with a spreadsheet?  Answer: if I am sufficiently clever,
> yes.
> Spike, are you sufficiently clever, and feeling enormous satisfaction with
> this whole discussion?  Answer: definitely.  {8^D
> So interested was I in that question, I took the thing home and had my Apple
> Mac2 grind on it for several days.  Fun little project.  That actually
> predated Excel macros.
> I still have that atmosphere model.  Keith, that is the sheet I used to
> discover that minor error in your friend Herr Doktor's Neptune paper from
> 1970, remind me his name?
>  spike
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Spike, have you checked out Google Doc's spreadsheets? Less features
than Excel, for sure, but the scripting language can touch everything
on the web (think: real time feeds from live data "out there") and
they appear to be a lot safer and easier in a multiuser context. I
think you'd like them.


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