Problem 780. Give a matrix that matches itself when rotated

Created by Ned Gulley
Appears in Sequences and Series VI

Difficulty:Rate

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Given n and s, return a n-by-n matrix a of integers such that

 sum(sum(a == rot90(a)))

is equal to exactly s. The integers should be chosen from the set 1 to n.

So for instance, if n is 2, and s is 2, you could return

 a = [ 1 1 
       2 2 ]

since rot90(a) matches a in exactly one place.

For any n and s, a is of course not unique. I'm only checking to make sure the conditions are true.

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Last Solution submitted on Feb 04, 2025

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Richard Zapor on 16 Nov 2012

s=feval(@evalin,'caller','s');

Lack of s input solved

Ned Gulley on 16 Nov 2012

Sorry guys. Sloppy problem creation on my part. Unfortunately my signature change will invalidate all the solutions up to this point, but yes it should be match_rot(n,s)

David Verrelli on 1 Dec 2017

"since rot90(a) matches a in exactly _two_ places" for the example in the problem statement?

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Problem 780. Give a matrix that matches itself when rotated

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Problem 780. Give a matrix that matches itself when rotated

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Last 200 Solutions

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Problem Recent Solvers13

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