POV-Ray : Newsgroups : povray.advanced-users : Stumped by desk lamp trig equation : Re: Stumped by desk lamp trig equation Server Time
2 Oct 2022 18:08:17 EDT (-0400)
  Re: Stumped by desk lamp trig equation  
From: Le Forgeron
Date: 15 Aug 2022 11:04:46
Message: <62fa608e$1@news.povray.org>
Le 07/08/2022 à 19:54, Cousin Ricky a écrit :
> On 2022-08-07 10:59 (-4), kurtz le pirate wrote:
>> On 06/08/2022 23:57, Cousin Ricky wrote:
>>
>>> Does this imply that I would need to program a numeric solution into my
>>> macro?
>>
>> I am afraid that it is not possible to solve literally an equation which
>> makes appear at the same time t, sin(t) and cos(t). A bit like in
>> differential equations with x and dx.
> 
> Then numerical computation it will have to be, albeit in SDL.
> 
>> Literal solutions never exist (except for school cases).
> 
> I suspected those examples in high school were conveniently contrived.
> 
>> Another trail.
>> Let sin(x) = T and cos(x) = U, the equation becomes :
>> (g - c/x)T + hU - a = 0
>>
>> Wolfram proposes a more "usable" result.
>> <https://www.wolframalpha.com/input?i=solve+%28g+-+c%2Fx%29T+%2B+hU+-+a+%3D+0>
>>
>> x = cT/(-a+gT+hU) with a!=gt+hU & cT!=0
>>
>>
>> Maybe more adapted to your needs ?
> 
> I'll take a look at it.  Thanks!

If you like complexity, remember that T²+U² = 1,
so U is actually sqrt(1 - T²), reducing the number of variables.
(of course for your setting T & U > 0)

Back to original problem, why is the c part a circle ?

If it is some flexible part, we are back to the evaluation of the length 
of a sphere sweep/spline for which there is no formulae, even when it's 
just a part of an ellipse.

Do you really need a fixed length c part ?

Can the right angle of the picture (base of light bulb or so) be on the 
y axis, with the c segment describing some S-like shape (or 
interrogation dot shape )

Why do I want that point on y axis ? Because it is probably better for 
the weight of the lamp to be correctly held.

Which make me wonder why there is a straight part after c, but not below it.


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