[Search for users] [Overall Top Noters] [List of all Conferences] [Download this site]

Conference rusure::math

Title:Mathematics at DEC
Moderator:RUSURE::EDP
Created:Mon Feb 03 1986
Last Modified:Fri Jun 06 1997
Last Successful Update:Fri Jun 06 1997
Number of topics:2083
Total number of notes:14613

1505.0. "Surface area on n-dimensional ellipsoid?" by ALLVAX::JROTH (I know he moves along the piers) Thu Oct 17 1991 09:49

    Now that the arc length of an ellipse is known...

    what is the surface area on an n-dimensional ellipsoid with axes
    a1, a2, ..., an?

    Can you give an accurate numerical algorithm?

    - Jim
T.RTitleUserPersonal
Name
DateLines
1505.1General arc length formulaCIVAGE::LYNNLynn Yarbrough @WNP DTN 427-5663Thu Oct 24 1991 20:1126
>    Now that the arc length of an ellipse is known...

In general, the arc length of the smooth continuous single-valued function
y=y(x) is given by 

	/
	|sqrt(1+(dy/dx)^2) dx
	/

>    what is the surface area on an n-dimensional ellipsoid with axes
>    a1, a2, ..., an?

... and for the area of the surface z = z(x,y) it's

	//
	||sqrt(1+(dz/dx)^2+(dz/dy)^2) dy dx
	//

and I think this generalizes easily to n dimensions.

>    Can you give an accurate numerical algorithm?

Not offhand! although any good numerical integrator should do... For 
ellipsoids it's probably necessary to use a parametric form 
{x=x(t), y=y(t), z=z(t)} since the derivatives dy/dx etc. are infinite at
the endpoints.