Problem 151. Magic!

Created by the cyclist

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Solution Stats

1983 Solutions
273 Solvers

Last Solution submitted on Nov 27, 2020

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Problem Comments

5 Comments

5 Comments

Show 2 older comments

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

anhendri 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.)

Solution Comments

Solution 1909426

1 Comment

1 Comment

Ivo Georgiev on 23 Aug 2019

tf=~any(sum(x-length(x)^2-1)+norm(x,inf)) the best

Solution 563857

2 Comments

2 Comments

Chellammai C on 23 Jan 2015

x = magic(2);
y_correct = false;
This is wrong!!!! hence solution failed

the cyclist on 27 Jan 2015

Although MATLAB does create a 2x2 matrix as an output from magic(2), that output is not a magic square.

Solution 61106

2 Comments

2 Comments

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

1 Comment

1 Comment

David Young on 22 Feb 2012

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

Solution 32908

2 Comments

2 Comments

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

1 Comment

1 Comment

wenwu xiu on 7 Feb 2012

passed in matlab but not here??what ??

Solution 28333

2 Comments

2 Comments

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

2 Comments

2 Comments

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

1 Comment

1 Comment

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

1 Comment

1 Comment

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.

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Problem 151. Magic!

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