[FRIAM] Optimization problem

Fri Sep 20 23:02:36 EDT 2019

You can splice together conduit pieces with set screw couplers.  They're
cheap, stable under compression loads, only require a screwdriver to
operate, and produce no toxic gases.

https://www.homedepot.com/p/Halex-3-4-in-Electrical-Metallic-Tube-EMT-Set-Screw-Coupling-25-Pack-62807B/202288563

-- rec --

On Fri, Sep 20, 2019 at 8:00 PM Carl Tollander <carl at plektyx.com> wrote:

> Welding galvanized steel without proper respirators (even outdoors) can
> kill you.  Research this carefully.
>
> How about some nice thick wall pvc?
>
> Carl
>
> On Fri, Sep 20, 2019, 17:48 Steven A Smith <sasmyth at swcp.com> wrote:
>
>> Gary -
>>
>> I understand better now...
>>
>> I definitely agree that the *most* naive eyeballing methods can be
>> excruciatingly wasteful.
>>
>> I presume that your conduit length requirements are not precise... that
>> you might be designing them to allow for leaving the window partially
>> open but otherwise not subject to intrusion or compromise?  That seems
>> to complicate the problem but may pose opportunities.  In particular,
>> *I* might be looking for solutions which leave me with a *minimum* of
>> leftover conduit by making them longer than their shortest possibles in
>> some cases.  Or looking at it the other way, even if you don't need to
>> leave the windows open much when "locked" a more complete use of the
>> material might be obtained by relaxing the length a little without
>> compromising security (if a given window can only be opened a few inches
>> for example).
>>
>> I will be interested in hearing the results of whatever optimization (or
>> satisficing) method you use yields.
>>
>> - Steve
>>
>> PS. regarding guerin's solution, an alternate would be to measure as
>> suggested, then cut naively until the remaining spaces are larger than
>> the remaining pieces.  Only *then* does one break out the welder and
>> begin to piece together as-needed.   I don't think these are equivalent.
>>   It also occurs to me that *2* pieces of conduit (end to end, unwelded)
>> in a window channel might be *nearly* as effective as a single piece,
>> albeit less elegant?
>>
>> > Hey Steve. The actual project is nothing elaborate. My house has a
>> > couple or three dozsen horizontally sliding windows with pretty weak
>> > locks. Since I've had a couple of break-ins in the past, I decided
>> > that the easiest way to shore up security for that aspect of the house
>> > is to just cut short pieces of 3/4 inch conduit to lay horizontally in
>> > the spaces where the windows slide. When I want to open a window, I
>> > will just stand its conduit piece up, and when I want to "lock" it
>> > again, just lay it back horizontally. I asked on FRIAM because instead
>> > of just eyeballing it and having lots of extra (even potentially
>> > useful in the future) pieces left over, I'd rather use my (and
>> > FRIAM's) brain to look at possible ways of optimizing this. Kind of
>> > fun actually putting my mind to something for a change (retirement can
>> > be boring if you're not careful).
>> >
>> > On Fri, Sep 20, 2019 at 5:55 PM Steven A Smith <sasmyth at swcp.com>
>> wrote:
>> >> Gary -
>> >>
>> >> I *patently don't* recommend my method, though it does have some
>> >> charms.   I recently was faced with a similar problem to yours where I
>> >> needed to cut and install trim around the perimeter of the room (with
>> >> door openings) I just layed hardwood floor in.
>> >>
>> >> Rather than go into it in detail (I already did that and realized it
>> was
>> >> a TL;DR as usual, so cut it) I will just say that I approach these
>> >> problems as *satisficing* and *constraint* problems rather than
>> >> *optimization*.    Once I had a candidate layout, I simply looked at
>> the
>> >> results and determined that the *waste* was acceptable.   Depending on
>> >> the circumstances I sometimes prefer to have for example, 2 3'
>> leftovers
>> >> rather than 1 5' leftover, other times, vice-versa, depending on how I
>> >> might use said leftovers in some future application (or hedging against
>> >> a mistake in my measuring/cutting).
>> >>
>> >> Care to share what your actual conduit/pipe project is?
>> >>
>> >> - Steve
>> >>
>> >>
>> >>> Thanks for the links, Peter. I will probably use that software or
>> >>> similar, to get a quick solution, then look at the MOOCs.
>> >>>
>> >>> On Fri, Sep 20, 2019 at 2:52 PM Pieter Steenekamp
>> >>> <pieters at randcontrols.co.za> wrote:
>> >>>> Two possible approaches are:
>> >>>> a) Solve the problem yourself. Use one or a combination of standard
>> algorithms ( eg you mentioned linear programming and greedy algorithms,
>> there are many more of course) and/or your own custom algorithm. If you
>> wish to go this route and want to learn about the subject, I recommend the
>> series of MOOCS by Stanford's Tim Roughgarden
>> https://www.coursera.org/specializations/algorithms
>> >>>> Or, I think yours is probably a knapsack -type problem and the MOOC
>> https://www.coursera.org/learn/discrete-optimization covers that
>> relatively well.
>> >>>> b) But if you just want to get the solution you can use optimization
>> software like
>> https://www.ibm.com/za-en/products/ilog-cplex-optimization-studio (they
>> have a free edition that will be good enough for your application) will
>> solve it for you without you necessarily knowing how the software does it.
>> >>>>
>> >>>> On Fri, 20 Sep 2019 at 21:00, Gary Schiltz <
>> gary at naturesvisualarts.com> wrote:
>> >>>>> I'd like advice on possible ways to solve the following problem
>> >>>>> (plumbers must surely face this all the time). I need to cut a set
>> of
>> >>>>> metal tubes of varying lengths from standard length (6 meter)
>> >>>>> galvanized conduit stock. The goal is to find the number of tubes I
>> >>>>> need to buy, and the order of cuts to produce the minimum amount of
>> >>>>> leftover, unused tube.  I'm interested in what types of solutions
>> >>>>> people use for similar 1-dimensional problems, e.g. linear
>> >>>>> programming, greedy algorithms, etc. (I've been Googling). I'm only
>> >>>>> looking to cut around 15-25 pieces, so my gut feeling is that an
>> >>>>> exhaustive search of all possible solutions, though probably
>> NP-hard,
>> >>>>> would be feasible to perform. Working programs, as well as libraries
>> >>>>> in any language would be a bonus.
>> >>>>>
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>> >>
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>>
>> ============================================================
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>> Meets Fridays 9a-11:30 at cafe at St. John's College
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>>
> ============================================================
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