Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

Edit : This question is better to be ignored until the following related question will be discussed enough.

This question relates to

I know "almost identical " is not mathematics. But if you have good mathematical words , please answer to my question. I learned (here StackExchange)I can compute an ellipse arc for my 2 end points and tangents at them. But I also learned there are possibly many other ellipse arcs of the condition. Then let me ask you whether these ellipse arcs are almost identical or not?

Thank you in advance.

share|cite|improve this question
You should wait till we discuss everything through instead of saying that "we are all saying right things and none of us is wrong". We're humans, we're not perfect, we might say wrong things. I don't think this question deserves to be answered right away. – Patrick Da Silva Feb 16 '12 at 7:37
Yes, I wait. But I just wanted to make sure that your algorithm is suitable for my particular purpose . – seven_swodniw Feb 16 '12 at 7:48
up vote 1 down vote accepted

My algorithm described in the previous answer characterizes an ellipse by its center two non-parallel tangents at two generic points on the boundary of the ellipse (generic points means the underlying vectors are linearly independent relatively to the center of the ellipse). Given those, "almost identical" means "they are the same set of points on the plane". If your tangents are parallel, you lose unicity ; the second parallel only gives information you already had with the first one, hence you need "new" information. That is because if you have a point on an ellipse and you know the tangent there, then the point at the opposite of the ellipse (going through the center with a straight line) has the exact same tangent. If you don't specify the center you will end up with different ellipses depending on where you choose to put this center.

Hope that helps,

share|cite|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.