How about these snapshots? q =: 21, 38, 55, 106
}.+/\inv q NB. 1st differences 21 17 17 51 +./}.+/\inv q NB. gcd of 1st diffs 17 NB. or 2 -/\ q _17 _17 _51 +./2 -/\ q 17 17|q NB. So, what is the required offset? 4 4 4 4 17%~ q-4 NB. what are the required factors? 1 2 3 6 Mike On 14/08/2018 07:07, Skip Cave wrote:
Attempting to solve the following Quora problem: What number must be subtracted from 21, 38, 55, and 106 each so that the remainders (technically differences) are proportional? Subtract the integers 0-9 from all four integers in the problem. Then find the prime factors of each set of four integers. Finally look for columns that have common factors in all four results: ]b=.q: each 21 38 55 106-/a=.i.10 ┌────┬───────┬────────┬──────┬──────┬───────┬─────────┬─────────┬─────┬─────┐ │3 7 │2 2 5 │19 │2 3 3 │17 │2 2 2 2│3 5 │2 7 │13 │2 2 3│ ├────┼───────┼────────┼──────┼──────┼───────┼─────────┼─────────┼─────┼─────┤ │2 19│37 │2 2 3 3 │5 7 │2 17 │3 11 │2 2 2 2 2│31 │2 3 5│29 │ ├────┼───────┼────────┼──────┼──────┼───────┼─────────┼─────────┼─────┼─────┤ │5 11│2 3 3 3│53 │2 2 13│3 17 │2 5 5 │7 7 │2 2 2 2 3│47 │2 23 │ ├────┼───────┼────────┼──────┼──────┼───────┼─────────┼─────────┼─────┼─────┤ │2 53│3 5 7 │2 2 2 13│103 │2 3 17│101 │2 2 5 5 │3 3 11 │2 7 7│97 │ └────┴───────┴────────┴──────┴──────┴───────┴─────────┴─────────┴─────┴─────┘ Now how can I write a J function that lists the column index in this array where all four sets of factors have at least one common factor? Spoiler - In the example, the 5th set (column index 4) has a common factor of 17. Skip Skip Cave Cave Consulting LLC ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
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