2011/9/26 Carnë Draug <carandraug+...@gmail.com>: > On 24 September 2011 23:33, JuanPi <ajua...@gmail.com> wrote: >> Hi >> >> >From a discussion in the IRC channel concerning this post >> http://stackoverflow.com/questions/242711/algorithm-for-index-numbers-of-triangular-matrix-coefficients/3148414#3148414 >> >> JordiGH improved the algorithm and include it in sprandsym, though he >> mentioned that there may be problem with rounding real numbers. >> Therefore user deeego proposed the use of lookup. JorgdiGH mentioned >> that the two version had similar profiling times and that deego's >> suggestion was more robuts cause it doen't suffer form rounding >> problems. I wrote the function and I post it here >> >> function [r c] = ind2sub_triu (N, idx) >> endofrow = (1:N) .* (N - (0:(N - 1)) / 2); >> r = lookup(endofrow, idx-1)+1; >> >> c = N - endofrow(r) + idx; >> end >> >> %!test >> %! A = [1 2 3 4; 0 5 6 7; 0 0 8 9; 0 0 0 10]; >> %! [r c] = ind2sub_triu (rows(A),1:10); >> %! A_shouldbe = accumarray([r; c]',1:10); >> %! assert (A,A_shouldbe) >> >> %! assert(A,) >> >> Why to add this function? Among other things, the function offers an >> alternative to the duplicate_matrix function when passing from >> vech(A.') to A. It is also useful when a matrix of differences of many >> points is stored and queried. >> That is >> px = rand(3,1); >> py = rand(3,1); >> Rx = vech(bsxfun(@minus,px,px')); >> Ry = vech(bsxfun(@minus,py,py')); >> D = sqrt(Rx .^2 + Ry.^2); >> >> Which points are at least at distance d=0.2? >> d=0.2; >> idx = find(D>=d)'; >> [p1 p2] = sub2ind_triu(size(p,1),idx) >> >> Then p1 and p2 contain the label of the points that follows the criteria. >> >> -- >> JuanPi Carbajal > > Hi > > where do you propose to have this functions? In the general package? > > Carnë >
Sure, why not. Lets see if any dev has a better idea. If not, then I can upload a properly formatted version to the feature tracker. -- JuanPi Carbajal ----- "Complex problems have simple, easy-to-understand wrong answers." Murphy’s Law Book Two ----- http://ailab.ifi.uzh.ch/carbajal/ ------------------------------------------------------------------------------ All the data continuously generated in your IT infrastructure contains a definitive record of customers, application performance, security threats, fraudulent activity and more. Splunk takes this data and makes sense of it. Business sense. IT sense. Common sense. http://p.sf.net/sfu/splunk-d2dcopy1 _______________________________________________ Octave-dev mailing list Octave-dev@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/octave-dev
