How to concatenate matrices

Create a 4x4 magic matrix A. Use MATLAB to assemble a new matrix B. I'm not sure how to turn the 4x4 matrix A in to a 2x2 matrix B, where first row: A 2A, second row: A^2 A+2

    A = magic(4)
    B = [A 2A; A.^2 A+2]

Answer 1

[Pawel Jastrzebski]

You must have got an error message when executing - what did it say? That should be your first clue as to what's wrong with the code.

In your case, the multiplication sign is missing '*'.

A = magic(4)
B = [A 2*A; A.^2 A+2]

Output:

>> B

B =

      16     2     3    13    32     4     6    26
       5    11    10     8    10    22    20    16
       9     7     6    12    18    14    12    24
       4    14    15     1     8    28    30     2
     256     4     9   169    18     4     5    15
      25   121   100    64     7    13    12    10
      81    49    36   144    11     9     8    14
      16   196   225     1     6    16    17     3

[jake stan]

oh you're right! thanks. What's the difference between ".^2" and "^2"?

[Pawel Jastrzebski]

"." means it's an 'element-wise' operation. You need to have two matrices of the same size and the respective elements in them will be multiplied/divied/raised to the power.

If you ommit the "." it's considered as a normal matrix operation.

[Jan]

@jake stan: A.^2 squares the elements of the array A, while A^2 calculates A*A with the matrix multiplication.