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16-Pearl
Mar 1, 2024 1:18 AM UTC
Question

Mathcad Community Challenge March 2024 - Perimeter of an Ellipse

I am shocked that I have walked the surface of this planet for over 5 decades without realizing that there is no exact closed-form solution for the perimeter of an ellipse. In school, we learn the perimeter of shapes like triangles, squares, rectangles, circles, parallelograms, and so on, but I feel like schools and teachers conveniently skipped over ellipses.

(An ellipse, in case it’s been a while, is the set of points where the sum of the distances from two points – the foci – is a constant.)

 

DaveMartin_0-1709255800267.png

 

Your challenge, should you choose to accept it, is to correct that oversight. Create a Mathcad worksheet that:

  • Derives, depicts, or shows one (or more) of the various approximation formulas / methods for the perimeter of an ellipse.
  • Create a calculator whereby someone can change the values of the semi-major and semi-minor axis lengths in order to find the perimeter.
  • Create a 3D plot of the perimeter as a function of the ellipse semi-major and semi-minor axis lengths.

Although there is no exact solution for the perimeter of an ellipse, this is a fairly well-documented problem. Therefore, your documentation in your worksheet is key! This worksheet should be able to stand on its own and be understood by someone with a basic knowledge of calculus (since integrals and infinite series are involved).

Good luck and have fun!

 

Find the Mathcad Community Challenge Guidelines here!

 

35 replies

21-Topaz II
Mar 2, 2024 7:16 AM UTC

Hi,

File enclosed Prime Express 9.0

Cheers

Terry

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24-Ruby IV
Mar 2, 2024 8:21 AM UTC

@terryhendicott wrote:

Hi,

File enclosed Prime Express 9.0

Cheers

Terry


Ellipse-Prime.png

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24-Ruby IV
Mar 2, 2024 7:48 AM UTC

I once won such an argument a long time ago - I showed two ellipses (Mean) for which there is an exact formula for the perimeter. One of them is a circle, and the second - see the picture.
A more challenging and interesting problem is the Cassini Oval (gmean) and the Cayley Oval (hmean)!

Ellipse-4c.png

PS

“The race course was a large three-mile ring of the form of an ellipse..”

Leo Tolstoy. "Anna Karenina"

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24-Ruby IV
Mar 2, 2024 9:16 AM UTC
24-Ruby IV
Mar 2, 2024 10:58 AM UTC

More interest plot

зз.png

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19-Tanzanite
Mar 4, 2024 2:39 PM UTC

My attempt attached (excludes part 3 as 3D -plotting not available in Express).

 

(As I couldn't do the 3D plot in Prime Express, I decided to do it in M15 - see below.

The plot is really boring!).

 

Ellipse3D.png

 

Alan

 

 

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16-Pearl
Mar 4, 2024 4:32 PM UTC

Every problem deserves a numeric solution.  I'll leave the complicated derivations for the experts.  This was good enough for Archimedes so good enough for me too.  Bit too much to make the 3D plot at this time.

 

Prime 7 attached.

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21-Topaz II
Mar 4, 2024 4:46 PM UTC

Hi,

Am enjoying the posts so far so want to add a quick from 1st principles approach:

Capture.JPG

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21-Topaz II
Mar 6, 2024 3:03 AM UTC

Hi,

Just could not resist it.  A page of matrices and voila 3D plot in express.

Capture.JPG.

Cheers

Terry

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1-Visitor
Mar 8, 2024 8:32 PM UTC

This is one I couldn't let go.  This question is easily solved using polar coordinates:

AndrewK_0-1709936677308.png

 

Calculation speed can be increased using the ellipse's symmetry by limiting the integral between 0 and pi/2 and multiply that value by 4.  With a similar technique surface, moment's of inertia and so on are easily calculated.

 

All this is pretty basic, really.  The fun starts when adding parameters to the equation, for instance making Superellipses and even (far) beyond.  In the following article I made use of Mathcad Prime to illustrate the above: https://www.athena-publishing.com/series/atmps/issbg-22/articles/260/view 

 

Enjoy!

Bert Beirinckx

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19-Tanzanite
Mar 9, 2024 10:24 AM UTC

@Bert

EllipseForm.png

Alan

 

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Werner_E
25-Diamond I
Mar 9, 2024 10:47 AM UTC

@AlanStevens wrote:

@Bert

EllipseForm.png

Alan

 


 

"... which is exactly  ..."

exactly??  The perimeter of a circle can't be calculated exactly, either. 😞

The closed form for the circle circumference is actually a deception, because the infinite series is hidden in the constant pi, which we have invented for the  ratio perimeter: (2*r) for the ellipse with a=b=r.

So there is no real difference between the perimeter of a general ellipse and a circle other than the pi approximation key being available on every pocket calculator...

 

I, too, enjoyed Bert's article.

BTW, I nice video on the topic of the ellipse perimeter can be seen here on Stand-Up Maths channel: Why is there no equation for the perimeter of an ellipse

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19-Tanzanite
Mar 10, 2024 8:43 AM UTC

Val Ochkov has asked me to post this picture:

pir.png

 

Val says he has just been banned from the forum!  I hope that's just a temporary glitch as he's been a great supporter of Mathcad and the forum for years.

 

Alan

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Werner_E
25-Diamond I
Mar 10, 2024 5:29 PM UTC

I guess and hope that it is not a ban on the part of the forum operators, but on the part of the Russian rulers.
If this is true, the use of a VPN could probably help Val  to overcome this hurdle.
If not, maybe the admins can say something about it -> @unknown , @AndrewK , @Jaime_Lee 

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19-Tanzanite
Mar 11, 2024 8:59 AM UTC


@Werner_E wrote:

I guess and hope that it is not a ban on the part of the forum operators, but on the part of the Russian rulers.
If this is true, the use of a VPN could probably help Val  to overcome this hurdle.
If not, maybe the admins can say something about it -> @unknown , @AndrewK , @Jaime_Lee 


Seems to have been a forum ban (Val sent me the following image):

ban.png

 

I assume this was an automated system response.  Perhaps an actual PTC person could overturn it?

 

Alan

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15-Moonstone
Mar 10, 2024 9:42 AM UTC

A friendly hello to the puzzle group,
I only have MC14 available. Therefore I couldn't read all the posts. Therefore, here is just a reference to a very good approximation function for the circumference of the ellipse - it is Ramanujan's formula. I don't know of a better one from the literature. I have attached them, but I cannot provide the desired 3D plot. I'm asking for help here.

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21-Topaz II
Mar 10, 2024 11:50 AM UTC

Hi,

Your function uu() has two parameters so producing a 3D plot is simple with the matrix() function.

Cheers

Terry

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15-Moonstone
Mar 10, 2024 12:15 PM UTC

I use MC14 and therefore cannot load your file. Would you please reply in the appropriate file format? I haven't created a 3D plot yet. They were mostly vicious equations that I solved using equivalent minimum problems.

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18-Opal
Mar 10, 2024 10:52 PM UTC

 

Using Ramanujan Approximation.

ppal_1-1710113706155.png

ppal_0-1710116304140.png

From MARK B. VILLARINO

 

192_05.pdf (emis.de)

 

Nice plots already done - see    AlanStevens 

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DJNewman
19-Tanzanite
Mar 21, 2024 12:50 PM UTC

Reminder to everyone that we're now in the last one-third of March! Great participation thus far.

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