2011/9/26 Jordi Gutiérrez Hermoso <jord...@octave.org>: > On 24 September 2011 17:33, 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? > > I kind of like the idea of adding this as a "triu" or "tril" option to > sub2ind (and to ind2sub). I'm CC'ing the maintainers list to see if > this could be done or if it's a dangerous idea. > > - Jordi G. H. >
Hi, Was this behavior of sub2ind pushed? >From ML documentation, http://www.mathworks.com/help/techdoc/ref/sub2ind.html all arguments to sub2ind are supposed to be scalars or arrays. Therefore a definition of sub2ind ## @deftypefnx {Function File} { @var{ind} = } sub2ind (@dots{}, @var{type}) and a check for string varargin elements type_str = varargin{ cellfun (@ischar, varargin) } if !isempty (type_str) <Do the new stuff> <Transpose according to type_str == 'triu' or type_str == 'tril'> return end Maintains a behavior compatible with ML. -- 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-d2d-oct _______________________________________________ Octave-dev mailing list Octave-dev@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/octave-dev
