[FRIAM] Optimization problem

Fri Sep 20 19:48:16 EDT 2019

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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>>
>> ============================================================
>> FRIAM Applied Complexity Group listserv
>> Meets Fridays 9a-11:30 at cafe at St. John's College
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> ============================================================
> FRIAM Applied Complexity Group listserv
> Meets Fridays 9a-11:30 at cafe at St. John's College
> to unsubscribe http://redfish.com/mailman/listinfo/friam_redfish.com
> archives back to 2003: http://friam.471366.n2.nabble.com/
> FRIAM-COMIC http://friam-comic.blogspot.com/ by Dr. Strangelove