From: Mark Holm 
To: atm{at}shore.net
Reply-To: Mark Holm 


> Hereƒ ™s my question: Was I full of it?  Did I do the
> numbers wrong, misinterpret the results, and merely
> reveal my ignorance of what cell optimization is all
> about?
>


I think you are essentially correct.  PLOP produces superior cell designs
chiefly because of two factors: 1. It, reasonably accurately, models the
mechanical behavior of the glass.  Previous amateur methods (e.g. Hindle,
Chandler) ignored the mechanical behavior.  2. PLOP allows (if you leave
refocusing selected) fairly considerable parabolic deformation and
minimizes only the non parabolic part.  It turns out that the deformations
of a mirror on a ring of supports of appropriate diameter are largely
parabolic, so that configuration is optimal up to a moderately large size. 
Thickness of course plays a part.  If you look at the 9-point cell section
of my mirror cell design page
http://users.telerama.com/~mdholm/atm/cells/index.html you will see that
the optimum 9-point arrangement inverts as mirrors get thinner.  For the
thinner mirrors, the optimum is nearly a single ring of points.

To see the 9-point cell for your mirror that is an improvement over the
6-point cell, you need to turn on Variable Angles on Supports (or Allow
Angles to Vary).


> moving on to the topic of why Frank Lloyd Wright never
> designed a suspension bridge.

>


Great architect, poor engineer and usually too proud to work with a good engineer.

Besides, a major part of the success of a good bridge lies in the foundations.

I don't think Wright was too interested in caissons, excavating, etc.


Mark Holm
mdholm{at}telerama.com

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