What's the difference between {} and [] in MATLAB?

Question

>> A={1 2;2 3}

A = 

    [1]    [2]
    [2]    [3]
>> A=[1 2;2 3]

A =

     1     2
     2     3

It seems to me they are essentially the same thing?

Answer 1

{}'s are for cells. []'s are for arrays/matrices.

Answer 2

No. They are not at all the same thing. The only aspect that is the same is the resulting shape.

An array (that which you build with []) is something you can use to do linear algebra. One number in each element.

A = [1 2 3;4 5 6;7 8 9];
[3 5 7]*A*[2 3 5]'
ans =
   915

A cell array is a general container, that will hold any object, any matlab variable entirely in each cell. Thus we can create a cell array composed of elements of any shape and size.

C = {'The' 'quick' 'brown' 'fox' 'jumps' 'over' 'the' 'lazy' 'dog'};

C is a cell array with 9 elements in it. We can put any class of variable in there.

C = {'asfghhrstyjtysj', 1:5, magic(4), sqrt(-1)}
C = 
    'asfghhrstyjtysj'    [1x5 double]    [4x4 double]    [0 +          1i]

We could even create a cell array where each cell contains only a single scalar number. But there would be no real point in doing so, as we cannot do arithmetic operations using cell arrays.

Answer 3

[] is an array-related operator. An array can be of any type - array of numbers, char array (string), struct array or cell array. All elements in an array must be of the same type!

Example: [1,2,3,4]

{} is a type. Imagine you want to put items of different type into an array - a number and a string. This is possible with a trick - first put each item into a container {} and then make an array with these containers - cell array.

Example: [{1},{'Hallo'}] with shorthand notation {1, 'Hallo'}

It is unnecessary to put objects of the same type (doubles) into a cell array like in your example.