Hi,
A dirty trick to get the job done would be to ravel the matrix ( , ), solve
the 1d version of the problem and then get the "true" indexes with
something like (<.@%&200 , 200&|).
For example, if you needed to just find the max:
(<.@%&200 , 200&|) (i. >./) , m
where m is your matrix.

I know this isn't a nice way to solve the problem, but it should work.

Sebastiano

2014-10-07 6:37 GMT+02:00 Jon Hough <jgho...@outlook.com>:

> Project Euler 85: https://projecteuler.net/problem=85
> This problem is not really conceptually hard, but I am struggling with a J
> solution.I have solved it in Python:
> =============================================
> def pe85(larg, rarg):   count = 0       llist = range(1, larg+1)
> rlist = range(1, rarg+1)
>         for l in llist:         for r in rlist:                 count +=
> l*r
>         return count
>
> if __name__ == "__main__":      # test for 2x3 grid, as in question.    k
> = pe85(2,3)   print "Test value: "+str(k)             l1 = range(1,200) #
> 200 lucky guess     l2 = range(1,200)       bestfit = 10000 # just a big
> number     area = 0        for i in l1:            for j in l2:
>          diff = abs(2000000 - pe85(i,j))                         if diff <
> bestfit:                             area = i*j
>   bestfit = diff
>         print "AREA is "+str(area)
>
>
> ================================================The above script will give
> the final area of the closest fit to 2 million. (The python code may not be
> the best). Also I tested all possibilities up to 200x200, which was chosen
> arbitrarily(~ish).
> Next my J. I go the inner calculation ok (i.e. see the function pe85
> above). In J I have:
> pe85 =: +/@:+/@:((>:@:i.@:[) *"(0 _) (>:@:i.@:]))
> NB. I know, too brackety. Any tips for improvement appreciated.
>
>
> But from here things get tricky. If I do the calculation over 200x200
> possibilities I end up with a big matrix, of which I have to find the
> closest value to 2 million, of which then I have to somehow get the (x,y)
> values of and then find the area by x*y.
>
> The main issue is getting the (x,y) from the best fit value of the array.
>
> i.e. If I do pe85"(0)/~ 200, I get a big array, and I know I can get the
> closest absolute value to 2 million but then I need to get the original
> values to multiply together to give the best fit area. Actually I have
> bumped into this issue many times. It is easy enough in a 1-d array,just do:
> (I. somefunc ) { ])
>
> or similar to get the index. But for two indices the problem is beyond me
> at the moment. Any help appreciated.Regards,Jon
>
>
>
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