Talk:Jacobi eigenvalue algorithm

Mathematics Start‑class Mid‑priority

	Mathematics portal This article is within the scope of WikiProject Mathematics, a collaborative effort to improve the coverage of mathematics on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.MathematicsWikipedia:WikiProject MathematicsTemplate:WikiProject Mathematicsmathematics
Start	This article has been rated as Start-class on Wikipedia's content assessment scale.
Mid	This article has been rated as Mid-priority on the project's priority scale.

Bug!

Hi all! I've just tried to use the algorithm, but there's a BUG! The maxind method is totaly wrong. A correct one would be:
int maxind(int k)
{
int m = 1;
for (int i = 2; i <= n; i++)
if(abs(S[k][i]) > abs(S[k][m])) m = i;
return m;
}
I hope there are no more errors...

Fixed

Quality

I touched this article some time back, but I did not write it and do not vouch for it. When I discovered it, the article was a complete disaster; I fiddled with the formatting alone, which is not enough. Frankly, it might be better to delete it and start over. (Mea culpa; if I had left it ugly that might have happened already!) --KSmrq^T 13:43, 15 June 2007 (UTC)[reply]

Incorrect calculation of theta

I'm not at all famailiar with this algorithm, but there appears to be an error in the derivation of theta for a particular i & j.

Given that 0 = cos(2θ)Aij + 0.5sin(2θ)(Aii-Ajj),

tan(2θ) = 2Aij/(Aii - Ajj) is wrong. It should be: tan(2θ) = -2Aij/(Aii - Ajj) or, tan(2θ) = 2Aij/(Ajj - Aii)

I'd like some input before editing the article, however. Snrrub (talk) 08:24, 6 July 2009 (UTC)[reply]

I don't really know a lot about it either, though you seem to be correct. Looking at Gentle's books (such as this one, but he uses exactly the same material in other books), which is the same as the current version of the article. However he also makes other mistakes (claiming that only the 4 elements change), so perhaps we should find a better reference. —3mta3 (talk) 09:22, 6 July 2009 (UTC)[reply]