type if x is a square matrix statement

Hi, How do I write the script for "If x is a square matrix funcz will be the 0"?

Thanks!

[Jan]

A bullet-proof solution is not trivial. Therefore this question is more interesting than it looks like on first glance.

Answer 1

[Stephen23]

funcz = ~diff(size(x))

[Jan]

This fails for a [2,2,2] array.

[Stephen23]

@Jan Simon: not really, because Zhuoying Lin did not specify what should happen for ND arrays: it is pure speculation to say what funcz should be when x is an ND array.

[Jan]

@Stephen: You are right. "0 if x is square matrix" might or might not imply that 1 is replied otherwise e.g. for nD arrays. Anyway, Lin will find enough details in this thread to solve the problem.

We need ~ismatrix(x), because 0 is wanted as output. But then ~diff(size(x)) replies a vector for nD arrays and the && is not applicable. What about:

~(ismatrix(x) && diff(size(x)))

Then the short-circuting should avoid the evaluation of the 2nd part, such that the "&& needs scalar input" problem does not occur.

[Stephen23]

@Jan Simon: thank you, that is a tidy solution for ND arrays.

[Zhuoying Lin]

Never thought about this question can be such complex. I just start learning Matlab and THANK YOU all for your answers!

Answer 2

[Jan]

funcz = ~ismatrix(x) || (size(x, 1) ~= size(x, 2));

or with Matlab versions before R2010b:

funcz = (ndims(x) ~= 2) || (size(x, 1) ~= size(x, 2));

This rejects [0 x 1] matrices, but is is questionable, if an empty matrix can be non-square.

To reply funcz=0 for vectors:

funcz = (ndims(x) ~= 2) || all(size(x) ~= 1);

or with modern Matlab versions:

funcz = ~isvector(x)

Answer 3

[michio]

[nRow,nCol] = size(x);
if nRow == nCol
 funcz = 0;
end

[Zhuoying Lin]

Thank you that helps a lot!

I have one more question:

What if now x is a vector how should I code it?

[Jan]

This fails for a [4,2,2] array:

[nR, nC] = size(rand(4, 2, 2))
nR = 4, nC = 4

[michio]

Yes, it assumes that the array is 2D. Interesting thread :)