Problem 151. Magic!

Created by the cyclist

Check whether the input matrix is a normal magic square:

http://en.wikipedia.org/wiki/Magic_square

Output the logical value true or false.

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89 solvers submitted 750 solutions (8.43 solutions/solver).

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David Young on 22 Feb 2012

This could be improved with a better test suite. For example, flipud(magic(n)) is still magical, but most of the leading solutions would return false for this.

Geoff on 19 Mar 2012

Yes, test suite is substandard. Could have drawn from this: http://nrich.maths.org/1338

Cartix on 7 Mar 2013

Why is magic(2) not a magic square ?

the cyclist on 8 Mar 2013

I was not notified about some of the older comments, so was unaware of some of the weaknesses of the test suite, and the "gamed" solutions. I have substantially improved the test suite.

the cyclist on 8 Mar 2013

The MATLAB command magic(2), although it does produce output, is not a magic square, according to the definition. (There is no 2x2 magic square.)

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Solution 61106

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Dan K on 14 Mar 2012

I'm pretty sure test 5 is wrong. magic(3)+1: sum of every row, column, and both diagonals is 18

Kevin Holst on 2 May 2012

It's not a normal magic square if it's of size 3x3 and doesn't sum to 15. All rows/cols/diags must sum to n*(n^2+1)/2.

Solution 33008

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David Young on 22 Feb 2012

I don't think this checks the diagonals. Is that because it's not necessary?

Solution 32908

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Aurelien Queffurust on 10 Feb 2012

issame is from which toolbox ?

Prateep Mukherjee on 19 Mar 2012

($matlabroot)/toolbox/robust/rctobsolete/robust/issame.m

Solution 32069

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wenwu xiu on 7 Feb 2012

passed in matlab but not here??what ??

Solution 28333

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Trung Duong on 4 Feb 2012

Test 4 is wrong: y_correct should be = TRUE

David Young on 22 Feb 2012

No, test 4 is correct. magic(2) does not return a magic square.

Solution 27155

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Aurelien Queffurust on 10 Feb 2012

Hein? -348052801600 where does this number come from?!

David Young on 22 Feb 2012

Note that this gives the wrong result for magic(4). I suspect that this is tailored to the test set.

Solution 12509

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Mark on 8 Apr 2012

I like this since there is nothing in the MATLAB doc which guarantees that magic() produces a normal magic square. Is it necessary to also check both diagonals?

Solution 11823

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Peter Wittenberg on 31 Mar 2012

Folks, I don't get it. If you create z= magic(3)', that's a magic square. No surprise. If you then do an isequal with magic(3), you fail the test. Thus this and all solutions of this class are wrong, marked as correct only because the tests don't offer transposed magic squares as a test. The test vector needs to be fixed so all these solutions show us as not working.

Problem 151. Magic!

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89 solvers submitted 750 solutions (8.43 solutions/solver).

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