If you are interested, you might consider putting together a J lab on the subject.
This would: (a) Help you retain the concepts for yourself, and expand your understanding of them, and (b) Help convey them to other people, also. If this interests you, we can help point you at lab authoring documentation. We need some people interested in writing some labs because the new platforms (especially phones) have UI adaptations which need some fixing, for labs. Meanwhile, one of the more important issues for an author is finding a good reviewing audience to work with. (Even more important, of course, is writing stuff.) Thanks, -- Raul On Wed, Apr 23, 2014 at 1:52 PM, alexgian <alexg...@blueyonder.co.uk> wrote: > > The information and more are in the vocabulary page for %. > > Well, yes, but so tersely and compactly expressed that you have to know the > long answer before you understand it! I did look at the Vocab page, but > didn't "get it", that's why I posted. > > It needed Roger's somewhat more expanded explanation for those of us that > are somewhat slower on the uptake. That's why I said the Vocab could use a > touch up. It is NOT user friendly, more of an ultra-coded reference. Of > course, you might not see it this way, but I'd bet most newcomers would. > > And it's not as if there is a longer explanation somewhere else, is there? > Well, other than this thread, I mean... :) > > > > On 23 April 2014 18:17, Roger Hui <rogerhui.can...@gmail.com> wrote: > > > The information and more are in the vocabulary page for %. > > http://www.jsoftware.com/help/dictionary/d131.htm . > > > > > > On Wed, Apr 23, 2014 at 10:02 AM, alexgian <alexg...@blueyonder.co.uk > > >wrote: > > > > > Great info, thanks Roger. > > > If it was up to me, I'd DEFINITELY include that in the Vocabulary, is > it > > > even documented anywhere else? > > > > > > > > > On 23 April 2014 17:33, Roger Hui <rogerhui.can...@gmail.com> wrote: > > > > > > > %. x for a vector x is the same as ($x)$%.,.x, and the key expression > > is > > > > %.,.x, the "matrix inverse" of a 1-column matrix. b=.y%.x on a tall > > > matrix > > > > x is solving a least-squares problem, the coefficients b that > minimizes > > > the > > > > sum of squares of y - x +/ .* b . > > > > > > > > In addition, for a non-zero vector x, (%.x) +/ .* x is 1, a special > > case > > > of > > > > that (%.x)+/ .* x is an identity matrix, whence one can deduce that > for > > > > vector x, %.x is x%+/x^2. > > > > > > > > ] x=: 7 ?.@$ 100 > > > > 94 56 8 6 85 48 66 > > > > %. x > > > > 0.00362137 0.00215741 0.000308202 0.000231152 0.00327465 0.00184921 > > > > 0.00254267 > > > > (%.x) +/ .* x > > > > 1 > > > > x % +/x^2 > > > > 0.00362137 0.00215741 0.000308202 0.000231152 0.00327465 0.00184921 > > > > 0.00254267 > > > > > > > > M=: 7 3 ?.@$ 100 > > > > (%.M) +/ .* M > > > > 1 5.55112e_17 _2.77556e_17 > > > > _1.21431e_16 1 1.11022e_16 > > > > _4.85723e_17 1.94289e_16 1 > > > > > > > > > > > > > > > > On Wed, Apr 23, 2014 at 9:13 AM, alexgian <alexg...@blueyonder.co.uk > > > > > > wrote: > > > > > > > > > Just wondering: > > > > > %. 2 3 4 > > > > > 0.0689655 0.103448 0.137931 > > > > > > > > > > Which is fair enough enough at one level, I suppose, since the dot > > > > product > > > > > of the two arrays IS 1, but what system/equation is being solved > > here? > > > > > Obviously, there are infinite solutions. Why that one? > > > > > IOW, which "matrix" is being inverted here? > > > > > > > > > > Thanks > > > > > > > ---------------------------------------------------------------------- > > > > > For information about J forums see > > http://www.jsoftware.com/forums.htm > > > > > > > > > > ---------------------------------------------------------------------- > > > > For information about J forums see > http://www.jsoftware.com/forums.htm > > > > > > > ---------------------------------------------------------------------- > > > For information about J forums see http://www.jsoftware.com/forums.htm > > > > > ---------------------------------------------------------------------- > > For information about J forums see http://www.jsoftware.com/forums.htm > > > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm > ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
