My reference to Perl's output was of the solutions printed on the count lines such as this:
1: 2 27 28 2: 3 26 28 3: 4 25 28 ..... 60: 17 19 21 61: 18 19 20 Total 61 Raul, thank you so much for your other pointers on inspecting the arrays. I will have two more days after work going over all of that. It's amazing how working through this seemingly simple problem with your help has taught me more about J than the hours I spent just doing single bits from the J dictionary. What would be the best J book to go through the vocabulary in problem sets such as this? Rosetta code? J for C programmers? My son said that one of the students arrived at the correct answer of 61 without a computer. I can't believe this given the time it would require to go through the answer space via pencil and paper (28^3). Is there a closed form solution, or algebraic solution? Good night, it's almost 3 am here in Macau. Thanks, Rob On Mon, May 27, 2013 at 2:19 AM, Raul Miller <[email protected]> wrote: > On Sun, May 26, 2013 at 2:01 PM, Robert Herman <[email protected]> > wrote: > > I have worked through the solution arrived at by a few of you to better > > learn J, namely this one: > > > > +/,(57=x+/y+/z)*x</y*y</z > > > > In order to fully understand the way the matrix operations are carried > out, > > I minimized the answer space by making P = 13, and worked through the > > output (not shown for brevity's sake) of the following input lines I > placed > > in a project file (learning the IDE with this problem too): > > > > P =: 13 > > x =: >:i.4 > > y =: >:x > > z =: >:y > > > > 3 4 $ x,y,z > > > > (13=x+/y+/z)*x</y*y</z > > +/,(13=x+/y+/z)*x</y*y</z > > > > +/,((13=[+/+/)*[</]*</)~i.7 > > Since this is a rank 3 bit array, we can ask J to display it more > compactly. > > <"2 '.*'{~((13=[+/+/)*[</]*</)~i.7 > > We can also use this prefix to inspect some of the intermediate results: > <"2 '.*'{~([</]*</)~i.7 > <"2 '.*'{~(</)~i.7 > > That said, some interemdiate results are not bit arrays and are > perhaps best inspected directly: > (]*</)~i.7 > > > > Anyway, I was tempted to try and make the J program look like the Perl > > oneby using > > for. but I realized I was lapsing into old habits. My minimal programming > > experience is all with imperative languages or some Lisp too. My next > > question is how do you get the J program to print the solutions as in the > > Perl program? > > That's an open-ended question, since "as in" has a contextual and case > specific meaning. > > Personally, I usually try and understand intermediate results (usually > there is only one and I can just extract an expression which computes > it and see what it does with sample data. > > > In my 3 x 4 matrices of the reduced problem set, I could see > > how the 1's in the solution selection matrix set related to the original > 3 > > x 4 matrix of x, y and z rows. Without re-writing it, is there a way to > > index the solution? > > I am not sure what you mean by this. > > I mean, of course you can index the solution, but the solution has > only a single number. You can also rewrite the expression which > creates that solution and index from those results. But I feel like I > am not understanding your question. > > > One question that is on my mind is the tacit vs. explicit style. I am in > > love with the way you all distill the solution down to a tacit one-liner, > > just as a maths formula is simplified, however, I am starting to think > that > > if and when I revisit this problem in the future, it will take a bit of > > jarring to read it, translate it if you will. I am guessing for. loops > are > > very expensive cycle-wise and it would be just as easy to make words for > > phrases if I wish to preserve future readability. I am getting addicted > to > > the fast way of working in the J environment, and I am grateful to all > on this > > list for sharing their wisdom. > > I think that any time we delve into some area of computation that > leaving and coming back after an extended absence can leave us in a > jarring situation where we need to reacquaint ourselves with the > original topic. I do not know of any general cure for this, finding > good names for things, and good examples, can be fruitful. > > Thanks, > > -- > Raul > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm > ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
