[FRIAM] Optimization problem

Fri Sep 20 21:59:38 EDT 2019

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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