Re: Memory leak?
- Posted by jimcbrown (admin) Feb 13, 2014
- 3664 views
Really!
Yes, really.
OK, so we make a list of 112 stars with their (x,y) coordinates. - how accurate??
To 2.5 milliarcseconds, according to wikipedia: http://en.wikipedia.org/wiki/Tycho-2_Catalogue
We can have 111 stars as their first match, 110 stars as their second match = 112 * 111 * 110 = rather a lot more than 227,000 (where did that number come from?).
That's the formula for permutations, where order matters. We don't care about order here (e.g. 55,66,77 and 77,66,55 are the same star triplet to us), so we should be using the formula for combinations instead.
Permulations: 112!/(112-3)! = 112 * 111 * 110
Combinations: 112!/3!(112-3)! = 112 * 111 * 110 / 6 = 227,920
This is rather basic stuff: http://www.mathsisfun.com/combinatorics/combinations-permutations.html
Second: If the distance between s1 and s2 is small (ie very small in relation to the distance from the origin) how accurate is any measurement going to be?
Didn't you already ask this? Measurements are (supposedly) accurate to 2.5 milliarcseconds.
Third: how do you determine 3 points are collinear? That is given 3 points (x1,y1).. how will you determine they are collinear and not run into problems with dividing values by other values close to zero.
I imagine gwalters will use the same method that he used with edbc, as the determination of collinearity isn't affected by the change from edbc to Derek's method.
