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16-Pearl
March 1, 2024
Question

Mathcad Community Challenge March 2024 - Perimeter of an Ellipse

  • March 1, 2024
  • 13 replies
  • 19059 views

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!

 

13 replies

23-Emerald I
March 29, 2024

This isn't really a response to the challenge.  The attached sheet poses a slightly different question.

 

I started out to answer the challenge; seemed easy to simply integrate along the curve and easier to do it in polar coordinates:

Fred_Kohlhepp_0-1711713089477.png

For the ellipse posed in the challenge:  

Fred_Kohlhepp_1-1711713164090.png

Then I looked at the other responses. . . .

And went back and checked, did the same thing in cartesian coordinates:

Fred_Kohlhepp_2-1711713385372.png

So why won't polar work?

 

 

19-Tanzanite
March 29, 2024

Not the right expression for the kernel of the integral Fred.  Should be as follows:

ellipse.png

Alan

23-Emerald I
March 29, 2024

Thanks Alan.

 

For pointing out my error.  I suspected it would be clear once it was pointed out.

16-Pearl
April 1, 2024

The March 2024 Mathcad Challenge is now closed. Thanks, everyone, for participating in this challenge. Quite a lot of activity on this one. 

 

18-Opal
April 16, 2024

https://www.mathcad.com/en/blogs/community-challenge-perimeter-of-ellipse

Here is the write-up! Thanks again to everyone that participated!

 

Stay tuned for May...

10-Marble
July 29, 2024

Hi DJ Newman, 

 

I am not sure how to put this out to the PTC Mathcad community but here goes.

I know that the "community challenge for the perimeter of an ellipse" has ended but building on previous submittals, I though the attached might be of interest to the community. Especially in terms of the accuracy of the various methods versus numerical and symbolic solutions. See attached Mathcad Prime 10 results.  

 

Thanks

18-Opal
July 29, 2024

Cool worksheet! I appreciate it and I think the Community will too.