Why comparing matrices is not evaluated as boolean in Octave?

问题

Im new to Octave and playing around with the console.

why when comparing matrices, the expression is not evaluates as boolean :

example:

>> A=[1,2;3,4];     % creating 2x2 matrix
>> 5 == 5           % sample comparison returns true (1)
ans = 1

>> A(1,1) == A(1,1) % single element comparison returns true (1)
ans = 1

>> A == A           % returns 2x2 matrix ???
ans =

  1  1
  1  1

>> size(A == A)     % prove that the above returns 2x2 matrix
ans =

   2   2

回答1:

== is for element-wise comparison of two matrices. To check whether two matrices are same or not, use isequal.

回答2:

Sardar's answer is correct, but when it comes to computational time, I think that my alternative answer is better: You can as well check that all elements of the boolean matrix A == A are 1, i.e., that the sum of 1s in the matrix A==A equals the number of elements of A, i.e:

sum((A == A)(:)) == numel(A)

ans = 1

Where the operator (:) simply vectorizes the matrix A==A so that it can be added with sum(). Compare the two answers when you matrix is quite big, for instance by defining A = rand(1e4), the computation time is considerably different...

来源：https://stackoverflow.com/questions/53252570/why-comparing-matrices-is-not-evaluated-as-boolean-in-octave